Raid novice

speedyj · 30 Apr 2008 at 10:47

I have a Western Digital WD2500AAKS and would like to try a raid setup for both speed and redundancy. I assume that another WD250 is required and a 500GB drive also to enable me to do raid 0+1.

My mobo is the Asus P5K Premium wifi.

Any advice on known issues or what 500GB drive to use would be most appreciated.

Also is there any way I can do this without having to resort to a complete reinstall of Vista64.

wesley · 30 Apr 2008 at 11:16

RAID 0+1 requires a minimum of 4 drives

you're thinking of RAID 0 or 1

have a look at this site http://www.acnc.com/04_01_0_1.html

speedyj · 30 Apr 2008 at 12:09

Thanks, perhaps I should have highlited novice

speedyj · 30 Apr 2008 at 12:13

Raid 1 sounds fine for me, the WD drives are pretty fast anyway and the mirroring will give me the protection I want

Will a fresh install be needed seeing as it is mirroring and not striping?

Zarf · 30 Apr 2008 at 12:20

For speed and redundancy, you want a RAID5 array, takes a minimum of three disks, and you lose one disk's worth of space to provide redundancy. So three 250GB disks would give you a fast 500GB array, where any of the three disks can fail without you losing any data. Speeds are about the same as a Raid0 stripe.

As for a fresh install, you should be ok with mirroring, but you need to make sure that the raid drivers for your motherboard are installed before you try and clone it over, or windows won't be able to boot. The safest way is to install the drivers, take an image with Norton Ghost or similar and save it to an external drive, then build your array and put your saved image onto the new array. That's how you'd have to do it with a raid 5 setup.

brendy · 30 Apr 2008 at 12:26

4 disk raid 10 would work also. mirrored and striped meaning you can afford to lose a disk with no real problems.

stealthgeek · 30 Apr 2008 at 12:30

Zarf said:
For speed and redundancy, you want a RAID5 array

Hang on a minute - RAID 5 is 'OK' for read speeds, but motherboard controllers are notoriously terrible at write speeds (usually around 7MB/s - 10MB/s) since the parity information is calculated in software. A decent spec raid controller (in the £hundreds) would give acceptable write speeds. If its redundancy and speed you're after without spending too much, try RAID 10. It needs a minimum of 4 drives and doesnt have any parity calculations, so read/write speeds are fast. Some motherboard manufacturers add support for this RAID type, but try not to get it confused with RAID 1+0, as its totally different.

speedyj · 30 Apr 2008 at 12:52

Glad I asked

No seriously though, with storage so cheap it makes sense to add some redundancy to my system.

I need to do some proper research and understand the benefits of different raid types.

rpstewart · 30 Apr 2008 at 13:05

I'm going to do my usual stuck record act at this point.

Redundancy is not the same as a backup.

All you get from a redundant array (RAID1,5,10 etc) is the ability to keep operating in the event of a hardware failure. You have no protection from accidental (or malicious) deletion, file system corruption, controller failure, fire, flood or theft.

If you want speed and "redundancy" then there's nothing wrong with RAID0 and a decent backup strategy.

Zarf · 1 May 2008 at 02:08

Hang on a minute - RAID 5 is 'OK' for read speeds, but motherboard controllers are notoriously terrible at write speeds (usually around 7MB/s - 10MB/s) since the parity information is calculated in software. A decent spec raid controller (in the £hundreds) would give acceptable write speeds. If its redundancy and speed you're after without spending too much, try RAID 10. It needs a minimum of 4 drives and doesnt have any parity calculations, so read/write speeds are fast. Some motherboard manufacturers add support for this RAID type, but try not to get it confused with RAID 1+0, as its totally different.

I was under the impression that with modern CPU's write speeds with onboard/software RAID5 were fine.

Edit - after googling for ICH9R Raid5 benchmarks i found this for a 4 drive raid 5 array.

Code:

Drive       Write-back cache  Access time  CPU Usage (±2%)  Burst speed  Average read  Average write
...
64k Stripe  Yes               13.0 ms      7%               1216.3 MB/s  197.2 MB/s    141.6 MB/s
...

7% CPU seems perfectly acceptable to me for those write speeds.