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Confused about RAID..need some help

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July 24, 2011 7:17:02 AM

Hi All,

I am about to build my new system in about 10 years and am confused about raid. I will be using a 120 SSD as my windows 7 64 bit boot drive + OS applications and will have 1 hard drive..most likely a 500gb wd caviar black. Here are my questions:

1) I know I have to setup the ssd in AHCI in the bios but do I set my HDD to AHCI or RAID 0? WHat are the pros/cons to setting my hdd to AHCI or RAID0? For example, if I set my HDD to RAID0, I know it will allow me to install another HDD to the setup and both will operate faster. However, will I lose all the AHCI features if I set my single HDD to RAID0?

2) If I do decide to set my HDD to RAID0, do I do this before setting my SSD to AHCI? Is there a step by step guide someone can link me to or outline for me?

Much appreciated!

More about : confused raid

a b G Storage
July 24, 2011 7:24:34 AM

You can't AID0 a single drive. You can chose AHCI for both. You want to avoid raid if you don't understand it.
July 24, 2011 7:26:37 AM

So if I set both to AHCI then when I add a second HDD, can I switch it to RAID0? - Would this format the HDD already in my system?
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a b G Storage
July 24, 2011 7:32:35 AM

i suggest google for finding out what raid is, the different kinds and how it applys to you

for you, i suggest avoid raid and just leave the setting as AHCI for best results
a b G Storage
July 24, 2011 7:36:01 AM

I don't think you can run a single drive in RAID. You need at least two disks. Yes, when you add a second drive you'll lose your data. Even if you could run AID0 on a single drive, you'll lose the data when you install the second drive anyways. Half the data needs to be on both drives, so you'll lose it no matter what.

Apache agrees, just avoid raid.
July 24, 2011 7:36:56 AM

I have googled RAID and I understand the basic info (diff between RAID 0, 1, 5, 10, 0+1)..it's the details that I do not get...

Ie. Is it possible to switch from AHCI to RAID0 without the drive being formatted....

Is there a website you can suggest which explains that me?
a b G Storage
July 24, 2011 7:42:13 AM

Quote:
you'll lose the data when you install the second drive anyways. Half the data needs to be on both drives, so you'll lose it no matter what.


I suppose advanced controllers can build the array without destroying the data, but I doubt the ones built into motherboards is like that.

www.storagereview.com
a c 154 G Storage
July 24, 2011 6:25:57 PM

AHCI is a subset of raid. If you specify sata mode as raid, you will also get AHCI.

You want AHCI for the ssd so that it can get the "trim" command to keep the ssd at best performance.

If you specify AHCI as the sata mode, you will get the windows 7 drivers which pass along the trim command nicely. You will not be able to raid anything.
If you specify raid, you will get the Intel drivers, and the latest versions will pass on the trim command to a ssd that is not part of a raid array.

What to do?

I am not a big fan of raid of any kind in general.
The performance benefits of raid-0 are much overhyped, and generally not of any benefit to the desktop user.
Also, the use of raid-1 for protection is not a great idea.
The value of raid-1 and it's variants like raid-5 is that you can recover from a drive failure quickly. It is for servers that can not tolerate any interruption.
Modern hard drives have a advertised mean time to failure on the order of 500,000+ hours. That is something like 50 years.
With raid-1 you are protecting yourself from specifically a hard drive failure. Not from other failures such as viruses, operator error,
malware, fire, theft, etc.
For that, you need external backup. If you have external backup, you do not need raid

----------bottom line------------

I suggest you specify AHCI to begin with. Changing the sata mode later will require reinstallation of the OS unless you are comfortable with registry hacks.
July 24, 2011 6:39:17 PM

I will definitely go AHCI for my SSD.

You also suggest I specify AHCI for my HDD? If I add a second HDD, you are also saying that the benefits of raiding those two HDDS are not worth it?

I just want to know if I have that option to raid my 2 HDDS later on if I set my current single drive to AHCI right now...it seems like I will lose all my info on the first HDD drive no matter what I do.

Best solution

a c 154 G Storage
July 24, 2011 8:47:44 PM
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chillin15 said:
I will definitely go AHCI for my SSD.

You also suggest I specify AHCI for my HDD? If I add a second HDD, you are also saying that the benefits of raiding those two HDDS are not worth it?

I just want to know if I have that option to raid my 2 HDDS later on if I set my current single drive to AHCI right now...it seems like I will lose all my info on the first HDD drive no matter what I do.


AHCI has some benefits by itself. Hot plug capability and S.M.A.R.T. statistics for instance.
It is a mode of accessing the hard drive, and does not change the contents of the hard drive.

Yes, Raid is not worth it except for a very few situations, and there are not many. Raid will look wonderful in benchmarks, but that is not the type of hard drive processing we do.
If one part of a raid-0 array fails, then the whole array fails. That is not a big thing if you have backup. My take is to keep it simple until you have a problem that only raid can address.
There are hardware based raid cards that have lots of ram, and discrete raid processors that can improve performance, but they are very expensive.

What raid-0 does is put alternate stripes(32k to 250K blocks) of data on alternate drives. For small random access, like the os does, there is little value. For large blocks of sequential reading, then maybe. But only if your app does anticipatory read ahead, like the benchmarks do so that I/o to the read ahead block can be overlapped with the processing of the first block.

If you later want to change from AHCI to raid, You will need to reinstall the os because you will not have the raid drivers installed when you change.
The contents of the os drive will be ok, but you would have to find some way to pre install the raid drivers. I think it is possible, but that is more of an issue in the unknown than I want to deal with. If, in the future, you wanted to convert your single drive into a raid-0 drive, and installed a discrete raid card, or were to reinstall the os, then you could do so by cloning your original drive to a raid array. If you were to convert to raid-1(mirroring), I don't think you would have a problem since rebuilding a failed array is what raid-1 is for.

If all this seems overly complicated to you, then good. Why do it unless you have some objective in mind?

A SSD is great for the OS.

For better performance on the conventional drives, get a large(1tb) drive. WD black or samsung is good.
Larger drives are denser, and will have better transfer rates, particularly on the first used outer cylinders that can transfer more data per revolution.
July 24, 2011 9:03:43 PM

Best answer selected by chillin15.
July 24, 2011 9:04:28 PM

Cool, thanks for that. One final Q: Is a 2TB HDD better than a 1TB? I am looking at the spinpoint f3, what are your thoughts?
a c 154 G Storage
July 24, 2011 9:17:58 PM

chillin15 said:
Cool, thanks for that. One final Q: Is a 2TB HDD better than a 1TB? I am looking at the spinpoint f3, what are your thoughts?


I don't know specifically.
But, go to the web site for the hard drive, and try to find their spec sheet. It is usually a detailed document with performance information on it. It should include some number like maximum continuous data transfer rate. Sometimes that info is hard to find.

!