Help With RAID

[MattDLEA]

OK, I have my new servers.

8*300GB HDD's .

Just booted it up and got to the HP Smart Array Controller.

I can select the drives. But the options I have are RAID 6 (ADG) RAID 5 RAID1+0 and RAID 0. Also options to use one drive as a spare.

 

Any recommendation on how I should go about this? looking to visualise with either XEN server or Hyper-v as we nnow have 2 copies of server 2012r2 licenses so basically I have 2 boxes to turn in to 4 servers.

[Norphy]

RAID 6 is probably the "safest" option because it will allow for two drive failures. However, write performance is severely compromised.

RAID 5... well with 300GB disks it's probably just about OK. The danger with RAID 5 these days is that the bigger the individual disks, the higher the chance of a second failure happening when an array is rebuilding. Performance is better than RAID 6 overall but RAID 5 is generally discouraged these days.

RAID 10, the fastest of the lot but you lose 50% of your raw capacity.

Do not use RAID 0.

 

There is no right or wrong answer here, every option has its advantages or disadvantages. You need to weigh them up and make a decision as to what's best for you.

 

In an ideal world, I'd probably use a pair of drives in RAID 1 for the OS and RAID 10 the rest for VM storage. You may find 900GB a bit pokey though.

Edited March 10, 2015 by Norphy

[3s-gtech]

Be careful with your terms. Visualise means to 'form a mental image of' (or to use a document camera!) You want to virtualise.

 

Where are you intending to put the hypervisor itself? My personal preference is to have it on a separate device or array to any VMs - so a memory stick for ESXi, or a RAID 1 array of two drives for Hyper-V. Not sure how big Xen is as to what it'll fit on. I'd then put all drives into RAID 10, whether six or eight members available.

[MattDLEA]

Thanks for the replies.

I dont have an option for raid 1 only 1+0 would that do for the first raid for the hyper-v.

[fairm010]

I have ESXi installed on an 8GB SD card on our DL380p's motherboards.

[Norphy]

The minimum amount of drives you can have for RAID 10 is four. If the RAID controller really can't handle RAID 1 (and if it can't, WTF? Seriously. WTF?), I'd RAID 10 the lot and carve off an appropriately sized boot partition for the OS.

[localzuk]

It depends what you want out of it...

 

RAID 0 - dangerous

RAID 1+0 - nice and safe. Halves the amount of space you get, so from 8 disks you'd 1.2TB. You can potentially lose 4 of the disks, so long as they're all in the same "side" of the array. If you lose a disk from both sides, you've lost the array.

RAID 5 - 2.1TB, but you have a little less resilience, in that loss of 2 disks will be the end of the array guarenteed.

RAID 6 - 1.8TB. You can lose 2 disks without losing the array. Losing a third will kill the array.

 

Hot spare - I personally don't like this idea. Having a disk that automatically kicks in without intervention means you can potentially lose the array during rebuild without having a chance to run a emergency backup.

[MattDLEA]

?

[3s-gtech]

Ah, I have seen that RAID setup utility before. In that utility, a two drive RAID 1+0 is actually RAID 1 (IIRC).

[Norphy]

Odd. According to the P800 product page, RAID 1 should be a thing

 

HP Smart Array P800 controller - Overview & Features

 

Is there a firmware update available?

[PotNoodleTech]

"Raid 1" only consists of two disks. Once you move up to 4 or 6 or 8 disks it automatically becomes Raid 10 as it automatically stripes both sides of the mirror to give you either 2+2 or 3+3 or 4+4 disks.

 

Possibly (probably?) if you only had 2 disks in there it would give you the option for Raid1.

[zag]

8x300gb drives!!!

 

With that many disks, there has a huge chance of failure!

 

Why so many drives? I'd go with RAID 6 as its probably the safest.

[localzuk]

8x300gb drives!!!

 

With that many disks, there has a huge chance of failure!

 

Why so many drives? I'd go with RAID 6 as its probably the safest.

 

No, there isn't a "huge" risk of failure. 300GB drives are small enough that they more than likely won't have any URE type errors on a rebuild, and 8 disks isn't a particularly large number anyway. In RAID 6, the upper limit is about 20 disks. RAID 5 is about 10. This is constrained by rebuild speed to be honest though.

Edited March 11, 2015 by localzuk

[PotNoodleTech]

I've got 16 x 146GB drives per server.

 

As with everything in live, the more the merrier!

[Sephiroth]

In addition to what everyone else has said, the only other thing to consider is how much space you'll need for your VM storage.

 

Assuming that you'll be assigning all disks to storage, with OS on a separate medium, the following configurations will yield these usable capacities.

 

R1+0: 1.18GB

R5: 1.89GB

R6: 1.62GB

R0: 2.16GB

 

This is based on usable disk space of 90% of the drive.

 

My advice would be RAID 5 with a good backup solution.

[mcolbourn]

I would have to say go with one big RAID 10 and don't have a separate array for the OS (Just create a small partition for the OS) If it is going to be a VM host server you need as many spindles working for you in both reads and writes.