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Basic RAID Questions!

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  • NAS / RAID
  • Hard Drives
  • Basic
  • Storage
Last response: in Storage
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May 28, 2007 4:45:23 PM

Hey guys,

I'm considering going for a three hard drive, RAID5 array along with my next major computer upgrade, because I've had many a failed hard drive! I know more or less how it works, but have a couple of basic questions on it...

1. With onboard RAID controllers that offer RAID5, how heavy are the parity calculations, as I'm guessing they're handled by the CPU? I'm weighing up whether I should consider a separate RAID controller or just use an onboard one.

2. Would my three hard drives then only work with the particular RAID controller that formated/set them up? Just wondering if I could substitute the motherboard/RAID controller if something went wrong, and keep all my data in tact.

3. How does the process of drive reconstruction take place, having replaced a failed drive with a new one? I know in terms of reversing the parity calculations, but does this happen during the POST?

May seem very basic questions, but I'm paranoid about this stuff when it comes to protecting my stuff!!

Cheers

More about : basic raid questions

May 28, 2007 5:15:08 PM

Ok, well, here's the jist of it. Your onboard RAID controller... what is it? Give me details, what kind of CPU art you going to have?

Although in all honesty you could just get a cheap little RAID 5 controller and have plenty of safety right there. I think they should a few SATA PCI-e RAID controllers on newegg that can save you a bundle.

As for the intercompatibility between RAID controllers, I wouldn't bet on it, sometimes they work, sometimes they don't. The reconstruction process happens after a boot-up, some will auto-rebuild, some won't, but they'll usually tell you when they're rebuilding. Hope this helps.
May 28, 2007 6:16:07 PM

I'm not sure what on-board RAID controller I'll have... but I'm probably going for a Core2Duo E6X00 processor - so whatever its supporting motherboard has I guess. But if separate ones aren't too expensive, I'll get one - although interoperability would be a good thing, in case I decide to change RAID controllers somewhere down the line. I wouldn't want to have to reformat the whole array, because I won't have anywhere to back that much stuff up.
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May 28, 2007 6:33:25 PM

Hmm... well I'd say that you've got a pretty powerful controller right there, and your CPU is one of the more performance-oriented ones so you could go with that. On the other hand... if you decided to switch to a dedicated controller you'd probably have to go with an adaptec since I'm almost certain that's who makes RAID controllers for Intel. When migrating from onboard to dedicated I will tell you this, BACKUP, RAID is not a substitute for backup.
May 28, 2007 7:09:48 PM

1 - they are heavy with RAID 5, so get a separate controller
2 - the hard drives only work with the controller, so if you changed controller you'd have to reformat and start again
3 - there is a utility that appears after POST that will tell you that there is a problem, and when you replace the faulty drive with a new new you will then be able to rebuild the array at the same screen

My advice is not to bother with RAID though - it is no substitute for a good backup strategy. In a commercial environment where having minimal downtime is an issue mirroring / RAID 5 is a good idea but not for the home user.
June 1, 2007 10:23:39 PM

Quote:
... if you decided to switch to a dedicated controller you'd probably have to go with an adaptec since I'm almost certain that's who makes RAID controllers for Intel. ...

Actually, the good quality dedicated controller cards come from companies like 3ware.
If you don't want to pay the $300+ price of a decent new controller card, consider buying a used one on ebay. I picked up a 4xIDE card for around $70 and used it to set up a RAID 5 system.
June 1, 2007 10:57:26 PM

RAID 5 has no place on the desktop, trust me I've ran it for years and finally decided to switch to RAID 0, why? Because even with RAID you still need to back up important data, if you get a virus etc then raid isn't gonna protect your data in anyway, if you delete a file by accident RAID won't help. RAID is not meant for a replacement for backups, it's meant to prevent downtime.

If you do decide RAID is still right for you, definitely get a dedicated controller, I've used both types and I can tell you that onboard RAID 5 sucks terribly.
June 1, 2007 10:57:43 PM

I'm not saying he can't go with a 3Ware, they're great cards, but what I'm saying is that if he did decide to switch from onboard RAID to a dedicated controller his best bet would be adaptec since if I remember correctly they make the onboard RAID controller for the ICH8R chipset (correct me if I got the chipset wrong, I'm a bit dislexic sometimes)
June 1, 2007 11:01:23 PM

I'm not gonna debate this. For performance you don't want RAID 5, and it's true RAID isn't a substitute for back up. I have to tell my dad that all the time. I always tell him to backup but he doesn't listen. Anyways to the OP, does throughput matter to you? What about availability? If you're just looking for uptime then RAID 5 is fine, just don't expect it to be fast. If you do go RAID 5, although I'd just say go RAID 0 or 10 with a backup, get a dedicated controller.
a c 186 G Storage
June 1, 2007 11:23:26 PM

For a good detailed discussion of raid and other storage issues, go to www.storagereview.com With a hard drive mean time to failure of over 1 million hours, you must have been very unlucky.
June 2, 2007 12:06:16 AM

I have some questions about raid 5 also

1. I have a 300 gig HD right now and wish to purchase 2 others just like it to get raid 5 of course, will I have to format my original? (i'd rather not)

2. If I reformat my boot partition, will my raid setup be fubar'ed?




I have a abit quad gt w/ jmicron raid controller.
June 2, 2007 12:16:19 AM

Quote:

1. I have a 300 gig HD right now and wish to purchase 2 others just like it to get raid 5 of course, will I have to format my original? (i'd rather not)


Usually no. Most controllers will allow you to migrate 1 drive into an array.

Quote:

2. If I reformat my boot partition, will my raid setup be fubar'ed?


I'm not sure what you mean, but basically the array will appear to the OS to be a single standard drive, and function the same.


And performance will suck with onboard RAID so if speed is an issue definitely look into a dedicated controller.
June 2, 2007 12:26:53 AM

i believe (anyone care to say otherwise) that my abit quad gt's raid is quite fast??!? I don't know from experience, but i've been reading nothing but goodness.
June 2, 2007 3:06:50 AM

Quote:

1. With onboard RAID controllers that offer RAID5, how heavy are the parity calculations, as I'm guessing they're handled by the CPU? I'm weighing up whether I should consider a separate RAID controller or just use an onboard one.


It depends... If you have tons of money, of course get a good add-on controller. If you have very high CPU processing requirements concurrent with data access, especially writing, then get a good add-on controller.

RAID 5 does have the highest CPU utilization (when it's under load and performing well -- if the RAID 5 performance is really poor, it'll be because of high drive access, not because the CPU is maxed).

Quote:

2. Would my three hard drives then only work with the particular RAID controller that formated/set them up? Just wondering if I could substitute the motherboard/RAID controller if something went wrong, and keep all my data in tact.


RAID is not a formal standard with compatibility specs, etc. You cannot in general cross vendors and have your RAID arrays accessible. Sometimes you cannot even cross RAID versions from the same vendor.

However, Intel has a good reputation of maintaining compatibility, and nVIDIA does that too. Provided that you stick to the same chipset type, and your original RAID data set uses no features that are unsupported in the target RAID implementation, and the vendor hasn't gone out and specifically broken compatibility, then you can detach the drives from one RAID implementation, attach them to a similar second implementation, and have your RAID array successfully recognized.

Note here that it's not so simple to take a working OS and its driver set on one motherboard and connect it to a different one and expect it to work perfectly. For this reason among others, keeping the OS separate from large/complex data sets is encouraged and done in practice.

Quote:

3. How does the process of drive reconstruction take place, having replaced a failed drive with a new one? I know in terms of reversing the parity calculations, but does this happen during the POST?


Redundant RAID is best considered as an uptime preservation tool. So you can have a system running with a failed drive. Similarly you can have a RAID reconstruction in progress with a replacement for the failed drive. Rarely would you want to be stuck in the POST phase while this is happening. With a good implementation, you should be able to start a reconstruction, work with it, even shut down the computer in the middle of the reconstruction, and then restart it. Shutdowns are sometimes uncontrollable -- to have a reconstruction which is so fragile that it cannot survive one is not a good design. (That said, sometimes drives fail exactly during a power cycle, and RAID reconstruction is a vulnerable period, so I'd take as few unnecessary risks as possible during this phase.)


Quote:

May seem very basic questions, but I'm paranoid about this stuff when it comes to protecting my stuff!!


If you're really paranoid, you should see that RAID, no matter how good, will not really protect your data. If everything goes well, it can protect you from a single drive failure. For everything else, and even RAID maintenance and upgrades, etc., you should have an external backup.
June 2, 2007 3:28:56 AM

ok, that being said, if i want to un-raid a drive, can I?
June 2, 2007 3:59:03 AM

Quote:
ok, that being said, if i want to un-raid a drive, can I?


There's a logical problem going from a large RAID array to a small one (or a single drive), so it's generally not supported as a conversion, and you need to figure out something for yourself -- typically, using backups.

You can detach a single drive, and if you have a RAID 5 setup, it'll keep on truckin', albeit slowly. Then you can take that drive, attach it to an external enclosure, and use it to backup some of your data. Repeat with another external drive if needed, and finally "un-RAID" the original array completely. Hopefully your OS wasn't on the array, otherwise you might have problems with the backup and re-boot.

One exception is RAID 1 (and here you don't change effective data size), which is so close to a single drive that with one drive missing it can often be treated as a simple single drive.
June 2, 2007 4:00:14 AM

Quote:
Usually no. Most controllers will allow you to migrate 1 drive into an array.

Quote:
ok, that being said, if i want to un-raid a drive, can I?


Newer Intel chipsets allow you to go from a single drive to Raid 1 or 0 but not 5 and back to JBOD. 680i and the P5N32-E Plus (due to using the same southbridge) allow you to go back and forth between Raid settings but not from JBOD. That's onboard Raid I'm not sure about add-on cards.
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