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VERY slow raid 5 - why?

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March 19, 2007 3:54:31 PM

Background:
I've had two disks in raid 0 for a while. They were lightning fast.
One of them started to crash. I got some service on the machine and it's now returned to me with three disks in raid 5.

Problem:
The disks now seem amazingly slow. I tested by copying a file of the size 700mb from one folder to another and it took five minutes!!
I also notice how slow it is when changeing song in my winamp playlist. It takes a swhole econd for each song to display in the playlist. So after changing song it takes about 40 seconds for the playlist to visually update.

Something is obviously wrong. I don't know anything about raids but surely this is not OK.

Any thoughts is appriciated, thanks!

More about : slow raid

March 19, 2007 4:33:36 PM

Quote:
it's now returned to me with three disks in raid 5.


Why aren't you asking this question of the people who performed unauthorized modifications to your system?
March 19, 2007 4:43:03 PM

what is the controller?
Related resources
March 19, 2007 5:15:24 PM

Quote:
it's now returned to me with three disks in raid 5.


Why aren't you asking this question of the people who performed unauthorized modifications to your system?

Sorry, I forgot to explain that I requested this modification.

I had originally planned to add a 3rd drive and do this but I never got around to it. Then when one of the drives started to fail I panicked and fortunately this company could save the data and add a 3rd.

I've contacted them and told them about my problem. It will take days until I get a reply though and on the off chance that I can fix this myself I wanted to consult with you guys here in this amazing forum.
March 19, 2007 5:19:08 PM

Quote:
what is the controller?


I don't know what that means...

However, looking around in my windows to see what's change I find something called Silicon Image ATA Controller. That might be what you're referring too?

When looking at the Hardware properties of my C: I see "Silmage SCSI Disk Device". If that's useful at all...
March 20, 2007 12:32:01 AM

ok, yeah thats what im talking about, it is a motherboard raid controller which is software based, so raid 5, wont perform well because the parity calculations are done by the main system processor.
March 20, 2007 12:43:42 AM

RAID 5 works best on a dedicated RAID controller.

Part of the problem could also be that they tried to change the striped array into a RAID level 5 array. I'm not sure what they did, but if you want to try RAID 5, I'd suggest backing up your data, reformatting, and reinstall everything on a RAID 5 array that you started from scratch.

If that doesn't work, get a RAID card. Newegg has some nice PCI SATA RAID cards for a reasonable price.
March 20, 2007 8:26:12 AM

Quote:
ok, yeah thats what im talking about, it is a motherboard raid controller which is software based, so raid 5, wont perform well because the parity calculations are done by the main system processor.


Aha, that makes sense.
But it worked perfectly as a raid 0.
Were there no parity calculations then?
March 20, 2007 9:05:48 AM

Quote:
ok, yeah thats what im talking about, it is a motherboard raid controller which is software based, so raid 5, wont perform well because the parity calculations are done by the main system processor.


Aha, that makes sense.
But it worked perfectly as a raid 0.
Were there no parity calculations then?

RAID 0 doesn't actually give you any redundancy so parity information doesn't even come into it. With RAID 0 all that happens is your data is split between two disks, so you get two disks reading and writing at once, hence the performance increase. RAID 0 is actually more failure prone than using a single disk because if either disk fails you lose your entire file system.

With RAID 5, whenever you write to disks the system also has to calculate parity information for the third disk whenever you write, which is why write performance is particularly bad with RAID 5 systems. Even on dedicated hardware RAID controllers you can have a multiple disk RAID 5 system and the write speeds won't approach what you can achieve on a single disk.

On a desktop system RAID 5 is a total waste of time. If you've got three disks I'd recommend you use the first 2 for a RAID 0 setup and use the third disk to backup data using some kind of automatic tool.
March 20, 2007 9:15:51 AM

Quote:

On a desktop system RAID 5 is a total waste of time. If you've got three disks I'd recommend you use the first 2 for a RAID 0 setup and use the third disk to backup data using some kind of automatic tool.


That sounds clever!

I was told that raid 5 would be just as fast as raid 0, but safer.
If this is not true, even with a raid card, then I think I'll do as you suggest.
March 20, 2007 9:35:04 AM

Quote:
I was told that raid 5 would be just as fast as raid 0, but safer.


I'm afraid whoever told you that was just plain wrong.

Quote:
If this is not true, even with a raid card, then I think I'll do as you suggest.


I've found Abakt to be useful for the backup tooling. Good luck with the config!
March 20, 2007 9:52:26 AM

With a high end RAID5 controller that does XOR calculations itself, a 3 disk RAID5 array should be just as fast as a two disk RAID0 array.

On a basic controller however, a 4 disk RAID 0/1 array will be faster on reads than a 2 disk RAID 0, and about the same speed on writes, but obviously requires your to buy another disk.
March 20, 2007 10:13:27 AM

Quote:
With a high end RAID5 controller that does XOR calculations itself, a 3 disk RAID5 array should be just as fast as a two disk RAID0 array.


I have LSI RAID controllers with hardware XOR calculations in a 5 disk + hot spare configuration and it is still slower on physical writes than a single modern SATA disk. However, the onboard cache speeds things up considerably until it gets full, which might be why you believe this configuration is faster than it really is.

Quote:
On a basic controller however, a 4 disk RAID 0/1 array will be faster on reads than a 2 disk RAID 0, and about the same speed on writes, but obviously requires your to buy another disk.


You may be correct but you may also start hitting limits with bus speeds with more than 2 disks. Plus, if you consider your basic RAID controller to be an onboard RAID controller, you will start getting significant overhead on your CPU.

My advice is to keep it simple.
March 20, 2007 11:19:36 AM

Quote:
With a high end RAID5 controller that does XOR calculations itself, a 3 disk RAID5 array should be just as fast as a two disk RAID0 array.


I have LSI RAID controllers with hardware XOR calculations in a 5 disk + hot spare configuration and it is still slower on physical writes than a single modern SATA disk.

Then something is terribly wrong. 5 disk RAID 5 with a dedicated controller should beat a single disk any day. My own experience and the tests I have seen all confirm this. I would say the choice depends on what you want to achieve. If you want to do RAID for desktop performance - then don't. RAID 0 is simply to dangerous (do you really always remember to backup?), and RAID 5 expensive for the performance gained.
If you need the capasity on the desktop, then by all means do RAID5 with a dedicated controller with hardware accelleration (use PCI-E 4x or 8x) (Also remember that SAS RAID controllers also can do RAID with SATA disks). Use at least 4 drives, and use as many to fullfill your space needs. A friend has 2 * 2TB RAID5 arrays in his desktop. And they perform very well - much better than any single drive ever did. When transferring data from his Raptor systemdrive unto one of the arrays, the Raptor is clearly the bottleneck.
March 20, 2007 11:43:27 AM

Btw, I think my drives are SATA 2, not scsi or anything else. If that matters?
March 20, 2007 11:50:41 AM

Quote:
Btw, I think my drives are SATA 2, not scsi or anything else. If that matters?


SATA2 is exactly what you should be going for Caintommy. SCSI is too expensive in a home system.
March 20, 2007 12:03:40 PM

Quote:
Then something is terribly wrong. 5 disk RAID 5 with a dedicated controller should beat a single disk any day. My own experience and the tests I have seen all confirm this.


Well my real world experience in the enterprise tells me otherwise. RAID 5 with 5 disks does offer better read performance but write performance which is RAID 5's weakest point is hard pushed to match a single disk. It may well do better under larger arrays (i.e. 10 or 15 disks) but for a small number of disks a single drive will write quicker. Besides which RAID 5 with 3 disks will "always" be slower then RAID 0 with two disks. With 2 disk RAID 0 you have to split the data in 2 and write to 2 disks, with 3 disk RAID 5 you have to split the data in 2, add parity data and then write to 3 disks in a striped pattern. RAID 5 with 3 disks is purely extra overhead and will always be slower!

Quote:
I would say the choice depends on what you want to achieve. If you want to do RAID for desktop performance - then don't. RAID 0 is simply to dangerous (do you really always remember to backup?), and RAID 5 expensive for the performance gained.


Your advice boggles me:

- RAID 0 is perfectly acceptable if you have a decent backup strategy. If you setup and automatic routine that runs once a week or requires a mouse lick then the fallibility of RAID 0 is perfectly acceptable
- RAID 5 is not a high performing system. You should never implement RAID 5 for performance. If you want performance and redundancy you should implement RAID 01 or RAID 10. You will never get decent performance from RAID 5 on a non-dedicate controller and even with a dedicated controller you are talking major expense.

If you ever deal with enterprise level database systems you will see that people like Oracle, Informix, etc.. describe RAID 5 is being a very slow file system for databases and this is precisely because of the poor write performance.

Quote:
A friend has 2 * 2TB RAID5 arrays in his desktop. And they perform very well - much better than any single drive ever did. When transferring data from his Raptor systemdrive unto one of the arrays, the Raptor is clearly the bottleneck.


Unsurprising as you are reading from the RAID 5 array.
March 20, 2007 12:19:09 PM

They seem slow because RAID0 is for performance which you were used to and RAID5 is for redundancy which is not performance. It is faster than no RAID but slower than RAID0.
March 20, 2007 12:32:32 PM

Quote:
A friend has 2 * 2TB RAID5 arrays in his desktop. And they perform very well - much better than any single drive ever did. When transferring data from his Raptor systemdrive unto one of the arrays, the Raptor is clearly the bottleneck.


Unsurprising as you are reading from the RAID 5 array.

Um, he said from the Raptor TO an array, which means the array is writing.
March 20, 2007 12:32:57 PM

Quote:
RAID 5 with 5 disks does offer better read performance but write performance which is RAID 5's weakest point is hard pushed to match a single disk. It may well do better under larger arrays (i.e. 10 or 15 disks) but for a small number of disks a single drive will write quicker. Besides which RAID 5 with 3 disks will "always" be slower then RAID 0 with two disks.
A friend has 2 * 2TB RAID5 arrays in his desktop. And they perform very well - much better than any single drive ever did. When transferring data from his Raptor systemdrive unto one of the arrays, the Raptor is clearly the bottleneck.


Unsurprising as you are reading from the RAID 5 array.


I said I was transferring FROM his Raptor UNTO the array. So the Raptor Reads and the RAID5 writes. And yes, I do not recommend 3 disk RAID5, but 5 disk RAID5 should perform much better than any single drive (read or write) and also beat a two disk RAID0. You don't need 10-15 disk arrays to have decent performance. If your experience is different, something else bottlenecks your system (controller, bus, blocksize etc.)

Quote:
I would say the choice depends on what you want to achieve. If you want to do RAID for desktop performance - then don't. RAID 0 is simply to dangerous (do you really always remember to backup?), and RAID 5 expensive for the performance gained.


Your advice boggles me:

- RAID 0 is perfectly acceptable if you have a decent backup strategy. If you setup and automatic routine that runs once a week or requires a mouse lick then the fallibility of RAID 0 is perfectly acceptable

I don't find the increased risk of RAID0 acceptable. Systems should be reliable first, fast second. Do you always remember to backup your desktop, every day/week? Anyway, I don't ever recommend RAID0.

Quote:
- RAID 5 is not a high performing system. You should never implement RAID 5 for performance. If you want performance and redundancy you should implement RAID 01 or RAID 10. You will never get decent performance from RAID 5 on a non-dedicate controller and even with a dedicated controller you are talking major expense.


I have both implemented and seen exellent performing RAID5 systems, and it's the best compromise between speed and cost, when large capacity is needed.
Yes, it needs a dedicated controller (and there is not a big difference in price between a good SATA RAID and a SAS RAID controller), and you need at least 5 disks (which can be SATA). So let me repeat: RAID5 is does not have good price/performance for desktop - except when you anyways need a lot of capasity.

Quote:
If you ever deal with enterprise level database systems you will see that people like Oracle, Informix, etc.. describe RAID 5 is being a very slow file system for databases and this is precisely because of the poor write performance.


I do work with large SAS arrays, and I have never heard any database companies recommend against RAID5, if there are enough disks. And write performance is excellent with a good controller. Yes, Raid 10 is even faster, but it costs a lot in disks.
March 20, 2007 12:37:34 PM

Google does not use RAID. Instead they have three backups for each HDD. They say that a RAID5 array of enterprise level SAS drives offers too high a risk of failure. It may seem cost in-effective at first, but when you consider the amount of money something as big as Google loses when a server failsyou begin to see that it makes sense. Sorry for the thread hijack but I just felt like throwing this in.
March 20, 2007 12:45:41 PM

Quote:
Google does not use RAID.

The software running Google is a very special distributed system (which I do admire). Designed for using many redundant cheaper systems instead of fewer, larger and more reliable (and much more expensive) systems.
In the end they have a more scalable and reliable total system, but it does need very specialized software, and it is not something you can implement generally.
March 20, 2007 1:03:33 PM

Quote:
Um, he said from the Raptor TO an array, which means the array is writing.


Oh yes, so he did, my bad. Very interesting this is then! So how could you tell the Raptor was the bottleneck? And did you take into any controller cache? I'm quite interested in this.

Quote:
I said I was transferring FROM his Raptor UNTO the array. So the Raptor Reads and the RAID5 writes. And yes, I do not recommend 3 disk RAID5, but 5 disk RAID5 should perform much better than any single drive (read or write) and also beat a two disk RAID0. You don't need 10-15 disk arrays to have decent performance. If your experience is different, something else bottlenecks your system (controller, bus, blocksize etc.)


Are you sure you're taking into account the drive cache? I find write speeds are lightning fast until the cache fills up and then things slow down considerably as the disk subsystem strains to keep up.

Quote:
I don't find the increased risk of RAID0 acceptable. Systems should be reliable first, fast second. Do you always remember to backup your desktop, every day/week? Anyway, I don't ever recommend RAID0.


Well, personally I have a network filesystem available and I make sure that I write all data I want to keep on that. But an automated routine is perfectly adequate, where's the hardship in scheduling a backup routine or double clicking a desktop icon every so often to do a backup?

Whether a system should be reliable first or not depends on what the system is for!

I have serious doubts whether a 5 disk RAID 5 system will beat two disk RAID 0 for write performance. For pete's sake it's all on the original post. This guy has 2 disks in RAID 0 and it was lightning fast and then had 3 disk RAID 5 and it was dog slow. Same hardware, different setup, and it's slower, that's what you'll get with any controller. RAID 0 will beat RAID 5, I challenge you to find some statistics or benchmarks that say otherwise!

Here's some sources that highlight the poor performance of RAID 5.

http://www.dbazine.com/datawarehouse/dw-articles/rittman8:
"RAID 5 can severely affect performance on highly updated databases."

http://download-west.oracle.com/docs/cd/B10501_01/server.920/a96533/iodesign.htm
When describing RAID 5:
"Sequential reads benefit the most, while write performance can suffer."
"Recent RAID 5 implementations avoid many of the traditional RAID 5 limits by installing large amounts of battery-backed memory (NVRAM)."

http://www.oracle-base.com/articles/misc/RAID.php?display_type=printable
This documents recommends the use of combinations of RAID 0 and RAID 1 over RAID 5 in all cases except where money needs to be saved.

http://www.dba-oracle.com/oracle_tips_raid5_bad.htm
Finally this documents highlights the flaws of RAID 5 for database performance and highlights that the recent advance that makes RAID5 viable in such situations is the onboard cache

And here's one more I added after my original post from Wikipedia
http://en.wikipedia.org/wiki/Raid_5#RAID_5
This just gives a general good overview about what I've been saying. In particular the RAID 5 Performance section backs up what I've been saying that whilst RAID 5 read performance is decent, "almost as good as RAID 0 for the same number of disks," the write performance is poor.
March 20, 2007 1:17:21 PM

How dare you quote me on things I didnt say! :p 
March 20, 2007 1:20:30 PM

Raid 5 with 3 disks is the slowest possible configuration for raid 5.

If you are going to run raid 5 you will need a much larger array.

Take it back and have the reconfigure for raid 0.
March 20, 2007 1:20:56 PM

8O Doh, sorry. That's what I get for trying to post in these forums and get my work done at the same time. You have no idea how many edits I made to my last post already!

I've corrected that leetle mistake.
March 20, 2007 1:27:35 PM

Quote:
Oh yes, so he did, my bad. Very interesting this is then! So how could you tell the Raptor was the bottleneck? And did you take into any controller cache? I'm quite interested in this.


Cache was not a factor due to dataset size (a copy of 50GB). The speed of the whole operation was equvalent to reading from the Raptor, and a copy from the first RAID5 array to the second array gave better performance than reading from the Raptor and writeing on the array.
Both arrays consists of 5 500GB 7200rpm SATA harddisks. Can't remember make or model of his controller.

Quote:
I have serious doubts whether a 5 disk RAID 5 system will beat two disk RAID 0 for write performance. For pete's sake it's all on the original post. This guy has 2 disks in RAID 0 and it was lightning fast and then had 3 disk RAID 5 and it was dog slow. Same hardware, different setup, and it's slower, that's what you'll get with any controller.


As you write he has a 3 disk RAID5 array. I don't dispute that a 3 disk RAID5 is slower than a 2 disk RAID0. Always will be, because in reality there are only data distributed over 2 disks in the RAID5 and there are parity to be calculated and written. A 5 disk array with a good controller shall beat RAID0, if correctly configured.
Anyways there are certainly something terribly wrong with his configuration. If it takes seconds to read ID3 tags from MP3 files in WinAmp, something has gone horribly wrong. The best advice is to reformat and experiment with different parameters, until performance is acceptable - but with 3 disks he won't reach RAID0 levels, and without a dedicated controller, writespeeds won't be optimal.

If you are a heavy Oracle user (with those expensive licenses), with databases which aren't that big, but accessed intensively, then money won't be a problem. If money is no problem, a massive RAID 1+0 with 15k SAS or fibrechannel disks will certainly outperform RAID 5 with a similar number of disks (but sacrificing capasity). But here we are talking a very special situation, and even here it will difficult to recommend the added expense if money has any importance at all.
March 20, 2007 1:44:42 PM

Quote:
Cache was not a factor due to dataset size (a copy of 50GB). The speed of the whole operation was equvalent to reading from the Raptor, and a copy from the first RAID5 array to the second array gave better performance than reading from the Raptor and writeing on the array.Both arrays consists of 5 500GB 7200rpm SATA harddisks. Can't remember make or model of his controller.


Ah, I think I might know why that's the case now. Whilst I was browsing through the source material I read that sequential writes can give reasonable performance on a RAID5 system but its random writes that are the problem. So this would make sense.

The following wasn't the original source I remember but it says the same. In fact if you want to know anything about RAID this site is excellent!

http://www.pcguide.com/ref/hdd/perf/raid/levels/singleLevel5-c.html

Quote:
A 5 disk array with a good controller shall beat RAID0, if correctly configured.


On the same controller RAID 5 with a larger number of disks may beat RAID 0 with a smaller number of disks, e.g. 5 disk RAID 5 over 2 disk RAID 0 (which I still think is disputable but I don't think we'll ever agree on that one) but 5 disk RAID 5 will always lose to 5 disk RAID 0.

Not that I'd ever ever recommend 5 disk RAID 0. 8O

At this point I think we are largely arguing about different things...... and got well away from the original post....

Quote:
Anyways there are certainly something terribly wrong with his configuration. If it takes seconds to read ID3 tags from MP3 files in WinAmp, something has gone horribly wrong. The best advice is to reformat and experiment with different parameters, until performance is acceptable - but with 3 disks he won't reach RAID0 levels, and without a dedicated controller, writespeeds won't be optimal.


Hmm, well it's most likely a controller configuration or quality issue. If the file system basically works but it is just slow then the basic RAID system is working so either there's some funky settings on the RAID controller or it's just naff.

Quote:
If you are a heavy Oracle user (with those expensive licenses), with databases which aren't that big, but accessed intensively, then money won't be a problem. If money is no problem, a massive RAID 1+0 with 15k SAS or fibrechannel disks will certainly outperform RAID 5 with a similar number of disks (but sacrificing capasity). But here we are talking a very special situation, and even here it will difficult to recommend the added expense if money has any importance at all.


This is true but my original already-off-topic point wasn't focussed on using databases, I was just using it to demonstrate what I was saying about RAID 5 write performance being bad. At the end of the day, you should never implement RAID 5 if you are focussed on performance, only if you want a large reliable and cost-effective filesystem.
March 20, 2007 2:09:55 PM

Quote:
Not that I'd ever ever recommend 5 disk RAID 0. 8O

Exactly - RAID 0 is a questionable idea with two discs, but as it goes from questionable to bad, and on to atrocious when adding more disks.

Quote:
This is true but my original already-off-topic point wasn't focussed on using databases, I was just using it to demonstrate what I was saying about RAID 5 write performance being bad. At the end of the day, you should never implement RAID 5 if you are focussed on performance, only if you want a large reliable and cost-effective filesystem.


Only in very special cases, have you only got one focus. Small highend Oracle databases where money is no object is one such case.
Generally RAID5 performs very well (not best) across a lot of usage scenarios, and starting with a good controller and 5 disks, it is also very performarnce/cost efficient. I am always balancing the requirements when making recommendations, and except for outlaying cases (very small systems or highend databases) RAID5 gives a lot of performance and capasity for the money. And it should certainly always beat single drives......
March 20, 2007 2:27:57 PM

To the OP: I'm running 4-disk RAID 5 on an Intel MB that has matrix storage functionality. My reads are lightning fast - which yours should be for loading a playlist. My writes are slow because I deliberately disabled the write back cache as I do not have battery backup.

If your RAID 5 array is currently rebuilding (there should be an icon in the system tray near the clock or something to indicate this), then your disk drive system will be slow. Also, if they configured your stripe size wrong, that can slow everything down as well.

The Silicon Image controller is indeed software-only. I use that controller on my MB for a RAID 0 array. It works ok for that, but I wouldn't consider it for RAID 5. The Intel controller (ICH7R) on my MB includes some circuitry to help improve the performance of RAID 5 and reduce the tax on the CPU. And with the writeback cache turned on, I do indeed get decent performance. Toms wrote a review about this a while ago comparing the ICH7R, ICH8R and nVidia 680i southbridges, and found the same.

So, check your MB to see what controllers it has on it. If it's a 955X, 965 or 975X Intel Express chipset, then you should have a controller better suited to RAID 5 already - but you will need to move your drives over to that controller and rebuild everything.

RAID 5 with 3 disks isn't a good idea, as other posters have noted. Consider getting a 4th and making it a RAID 10. It will be much easier to manage, and easier (and faster) to fix if a drive fails.
March 20, 2007 2:34:03 PM

Quote:
Exactly - RAID 0 is a questionable idea with two discs, but as it goes from questionable to bad, and on to atrocious when adding more disks.


Don't put words into my mouth. RAID 0 with 2 disks is a very good idea on a performance oriented system. RAID 0 with more disks is a very good idea on a specialised performance system.

Quote:
Only in very special cases, have you only got one focus. Small highend Oracle databases where money is no object is one such case.


- On filesystems where the focus is performance RAID 0 beats RAID 5.
- On small filesystems where the focus is reliability, RAID 1 beats RAID 5.
- On large filesystems where the focus is reliability, RAID 5 beats RAID 1.
- On large filesystems where the focus is performance and data security is also important, RAID 01/10 beats RAID 5.

There's about a million places on the web that say RAID 5 performance is less than other RAID levels and you accuse me of only having one focus? You seem to think RAID 5 is best for everything.

Quote:
Generally RAID5 performs very well (not best) across a lot of usage scenarios, and starting with a good controller and 5 disks, it is also very performarnce/cost efficient. I am always balancing the requirements when making recommendations, and except for outlaying cases (very small systems or highend databases) RAID5 gives a lot of performance and capasity for the money. And it should certainly always beat single drives......


Well from enterprise level experience I disagree! RAID 5 is not considered anything more than adequate for performance and should never be the focus for getting a RAID 5 system put into place. RAID 5 is a good system and is very widely used in the industry as it is a good "general purpose" solution. The irony is that I mainly use RAID 5 filesystems at work, even on some database servers, but that's because performance isn't an issue.

I'm bored with arguing about the RAID 5 vs single disk write performance. I did a load of benchmarks on a hardware controller about 5 years ago but I can't find the data.
March 20, 2007 2:37:04 PM

I have one 36GB SCA SCSI with a host adapter and two Western Digital Caviar 16MB 250GB. What is the IDEAL setup for performance on these 3 drives? I was thinking a stripe but that would mean the array is only as fast and big as the slowest/smallest drive. Is there a way I can maybe RAID the SATAs and boot from the SCSI? I want pure, no punches pulled, screaming perdformance. (With what I have)
March 20, 2007 2:58:53 PM

Ask me an easy one why don't you! 8O

You asked for a pure performance answer, it all depends on the capabilities of the RAID controller and what you mean by pure performance

If it's a good controller and you mean file transfer rate as being pure performance then creating a RAID 0 logical across the first 36GB of all 3 disks and a second RAID 0 logical disk across across the remainder of the 2 WD drives should give best performance.

If it's not such a good controller, i.e. it can't do the above configuration or performance across different drive types suffers, or by pure performance you mean random file access times, then you want to put the two WD disks into a RAID 0 array and leave the SCSI disk as a standalone disk. The RAID 0 array will give you best transfer rates and the SCSI disk will give you shorter random access times.
March 20, 2007 3:05:35 PM

So I should install the OS on the SCSI and everything else on the two SATAs? And even if the SCSI is not included in the stripe, I can still boot from it and use the SATAs right?
And would a PCI-e SATA RAID card be faster than onbaord SATA RAID? (eVGA T1 680i LGA775)
March 20, 2007 3:06:49 PM

Ok, then lets agree to disagree. But your point-of-view on RAID5 certainly seems strange from my years as a consultant and from what I have learned from for example HP's enterprice storage courses. HP recommends RAID5 for performance filesystems and databases, unless money is no object and the database is relativly small but heavy used.
March 20, 2007 3:15:54 PM

Quote:
I have one 36GB SCA SCSI with a host adapter and two Western Digital Caviar 16MB 250GB. What is the IDEAL setup for performance on these 3 drives? I want pure, no punches pulled, screaming perdformance. (With what I have)


Well if you don't care much about your data, or you are very good doing backups to DAT, LTO or external harddisk, then you should let the 36GB SCSI drive be system drive (no RAID) and the two WD drives be RAID0.

Quote:
So I should install the OS on the SCSI and everything else on the two SATAs?


Yes.

Quote:
And even if the SCSI is not included in the stripe, I can still boot from it and use the SATAs right?


Thats another yes. And when your SATA RAID0 goes poooff, then you can still boot your system. You can even experiment to your hearts content with different RAID stripe sizes, block sizes and other parameters, as you don't need to reinstall your OS every time.

Quote:
And would a PCI-e SATA RAID card be faster than onbaord SATA RAID? (eVGA T1 680i LGA775)


Depends. The 680i is not the best RAID, but then again, it's not that bad. And RAID0 is NOT very taxing from a controller point of view, so you should be ok with the onboard solution.
March 20, 2007 3:22:22 PM

Well I have a 6 port PCi-E SATA RAID Controller. I also have a few more SCSIs. I have 2 15k SCSIs and 2 host adapters. What Should I do? How should I use the 2nd one? Paging file? I have 2gb of RAM so i turned paging off.
March 20, 2007 3:42:37 PM

Quote:
Well I have a 6 port PCi-E SATA RAID Controller. I also have a few more SCSIs. I have 2 15k SCSIs and 2 host adapters. What Should I do? How should I use the 2nd one? Paging file? I have 2gb of RAM so i turned paging off.


Nice little hardware collection 8)

It's difficult to judge how your PCI-E SATA controller compares in RAID0 to the integrated controller. The advantage of the PCI-E RAID controller is typically in RAID5, but thats not what you are after.
I would:
Install one SCSI host adapter, and use one of the 15k SCSI drives as OS drive without RAID.
Use the other SCSI drive as swap drive without RAID.
Use the two SATA drives in RAID0 on the integrated RAID controller for everything else.
Save the PCI-E controller for later, when you buy those 5 * 1TB Hitachi SATA drives for that nice 4TB RAID5 array, to house your media collection :D 

I'm a bit in doubt if you have 3 SCSI drives (1 SCA and 2 68pin SCSI) or only 2. If you got 3, then install both hostadapters and use the SCA as systemdrive, and the two 15k SCSI in RAID0. That would be extremely fast.
March 20, 2007 3:48:33 PM

My collection includes a fairly large supply of 15ks and 10ks. Of course I am going to use the 15ks and I only have host adapters though. So one system drive (15k SCSI) one page/swap disk (15k SCSI) and two everything else disks (2x WD Caviar 16MB 250GB SATA). I don't have a SCSI RAID card. (They are all SCA)
March 20, 2007 3:54:02 PM

Can your host adapters run RAID0 ?
March 20, 2007 4:00:30 PM

Quote:
So I should install the OS on the SCSI and everything else on the two SATAs?


Well I'd recommend you use the 36Gb disk purely for backup, but if you aren't bothered about that I honestly don't know what would give better performance. The SCSI disk would like give better random access times, meaning accessing lots of small files would be quicker, but the RAID 0 array will give better throughput, meaning accessing large files would be quicker.

Quote:
And even if the SCSI is not included in the stripe, I can still boot from it and use the SATAs right?


Yes, this should definitely still be possible!

Quote:
And would a PCI-e SATA RAID card be faster than onbaord SATA RAID? (eVGA T1 680i LGA775)


I don't know. Intel's ICH RAID is fairly mature these days but some other onboard controllers aren't quite as good. Plus it depends one the quality of the PCI-e card. Your best bet is to try and find some benchmarks and look at performance and overhead because most onboard and I suspect some add-on RAID controllers are partially software based.
March 20, 2007 4:03:51 PM

Would a SCSI with a host adapter be better for gaming?
March 20, 2007 4:35:39 PM

Quote:
Would a SCSI with a host adapter be better for gaming?


SCSI beats anything not RAID, and SCSI RAID beats SATA RAID. Any 15k SCSI harddisk beats the Raptors, no contest.

Use one 15k drive as systemdrive (lots of small files in Windows), and if you have a SCSI/SCA host adapter supporting RAID0, then take another two 15k SCSI drives and make a RAID0 array for programs and data.

If not, then take a second SCSI drive to be swapdrive, and take the two SATA drives and use motherboard RAID0 to make a data and program drive. Remember to backup.
March 20, 2007 4:51:12 PM

Actually storagereview showed that the latest Raptors (ADFD) outperform all the current top 15K SCSI drives in a single-user scenario (including gaming). Something to consider!

Take a look here if you're interested, and the next page beyond that:
http://www.storagereview.com/articles/200601/WD1500ADFD...

Of course the Raptor loses in access times and sequential reads and writes (although is quite close on the latter), but as you can see it beats the SCSI drives hands down in the single-user tests. Since that article the only new SCSI drive worthy of mention was the Cheetah 15K.5 with perpendicular recording, but although it had HUGE read and writes speeds its single-user performance was poorer than the previous generation Fujitsu and Maxtor.
March 20, 2007 5:02:57 PM

Quote:
Would a SCSI with a host adapter be better for gaming?


SCSI would be nice, SAS is much better (Serial Attached SCSI).

And on the discussion here, I have RAID-5 setup with 3 SATA disks running at this time. I've did some benchmarks and compared it to the single SAS drive setup and 2 disk RAID-0 SATA disks. The final results putting RAID-5 with 3 disks very close to the RAID-0 in terms of reads and about 10% slower in writes, single SAS drive lost to both, though it performace was close and impressive. RAIDs were tested on the Intel's ICH-8R and SAS benchmark was ran on the blade server (designing them... so have access to the server hardware).

My view on this, you sacrifise a bit on the write performance with R5 but you get better reliability then R0. If you are going into 4 disk scenarios then the size comes into the picture.

The performance question of the post could be result of the few things:
1) One of the drives is failing
2) Improper RAID set-up (disk mismatch etc)
3) If it is based on software - may lead to 30-40% degradation of performance.
4) RAID table is not set up. There is some time needed to setup and buid parity table.
March 20, 2007 5:12:32 PM

Yeah, but name someone who can afford a SAS drive and a controller card...
March 20, 2007 5:15:13 PM

I think I will set up the following:
System Disk: 15k 36GB SCSI
Swap Disk: 16k 36GB SCSI
Programs: Western Digital Caviar 16MB 250GB (x2) RAID0 16kb
March 20, 2007 5:16:40 PM

Quote:
Yeah, but name someone who can afford a SAS drive and a controller card...


I can and it wwould be close to free =) I work with them and we get lot's of outdated but still good parts =). So 74G SAS and a nice controller SAS/SATA x10 might end up in trash any time....
March 20, 2007 5:18:36 PM

GOOD $HIT MAN! Better guard those cans... I am getting my SCSIs from work. Anyone wanna buy some? Free for me.
March 20, 2007 5:31:13 PM

Quote:
GOOD $HIT MAN! Better guard those cans... I am getting my SCSIs from work. Anyone wanna buy some? Free for me.



I really can't say that I would run SAS at home, it doesn't seem to ba a good option - strains the PCIx bus and puts some heavy load on the system, generally it might end up in a very low performance and the same would go to the SCSI controller. Besides, there always beed issues with OS where it will fail to recognise or use high end server grade controllers.
!