Best arrangement of 8 disks in a RAID array

[George_B]

I have just ordered an HP DL380 G5 and it is equipped with the P400 RAID controller with the 512MB cache and battery backup.

Attached to that will be 8 x 146GB 10k SAS HDD and I am trying to work out what would be the most suitable approach to configuring the disks. I have briefly read the benefits of having one large VMFS partition and of having a small VMFS partition.

The options that I have come up with so far are:

7 disks in a RAID 5 array with 1 hot spare giving a total of 876GB storage

2 RAID 5 arrays of 4 disks with no hot spare giving 876GB of storage

1 RAID 5 array of 3 disks and one RAID 5 array of 4 disks with one hot spare giving 730GB of storage

Now as far as I am aware the controller supports RAID levels 0,1,01,5,50 and 6

Does any one have any other ideas for configurations or comments on what I should be considering?

[Paul_Lalonde]

Well, you'll probably get 100 different responses, but with one common thought: do you want performance or capacity? or a mixture of both?

My recommendation for performance is RAID-10. My recommendation for capacity with performance is RAID-50.

Paul

[George_B]

The server is being used to consolidate a number of physical servers that are being used in a small communications room for demonstration purposes so will have very light load on them. Previously there have been issues with maintenance and older machines failing without people noticing so I was looking for redundancy and the idea of a hotswap to make sure the RAID rebuild was automatic.

Just to confirm, each array will be seen as one LUN to ESX ?

[acr]

We really only recommend RAID 1, 10 or 50.. (where possible)

RAID 1 for your ESX OS.

RAID 10 or 50 for your VMFS (VM's)

[petedr]

We have always been a fan of RAID 10, I was looking at the P400 specs and it says it does support Raid 10. However with an 8 disk Raid 10 array you don't have the hot spare which is also nice to have.

[George_B]

Acr

Would 146GB not be wasted for just the ESX OS ?

[JonT]

In his scenario there would be some extra space but you could have an extra VMFS volume on that first mirror to not waste the space. All of my stand-alone Hosts (non-SAN attached) have the drive configuration:

2x 72GB RAID 1 - ESX OS and SWAP

4x (or 6x in the G5 case) 146GB RAID 10 - VMFS

My SAN attached are only 2x 72GB for OS and Swap. I do not usually create the VMFS on local storage in that case.

Hope this helps some.

Oh and to answer an earlier question each Logical Drive is seen as a LUN in ESX. If you have more than one Logical per array you will see multiple LUN's for the local SCSI "hba".

Message was edited by: JonT

JonT

[George_B]

What is the limit on the number of VM vmdk's you can have per VMFS, 32 ?

So 3 drives in an array is seen as one Logical Drive and thus one LUN or as 3 LUNs for the physical drives ?

Message was edited by:

George_B

[acr]

No real limits as such, but you have to be aware of what your apps are doing etc..

Putting many VMs into a single LUN will give you SCSI Locking(reservation) issues..

So better to create multiple LUNs and share out the load..

http://www.vmware.com/pdf/tips_tricks_infrastructure_services.pdf

[George_B]

Thanks for the info.

[acr]

Your welcome, hope it helps.

[JonT]

acr is absolutely right about the SCSI locks. The number of VMDK's per "LUN" will vary depending on a lot of things.

Your 3 drives are in one array, but depending on your physical controller you can have 1 logical drive for that array or several. If you want to avoid the SCSI lock possibility for that same 3 drive array, you could consider creating 2 or more "logical drives" which would be seen as separate "LUN's" within ESX.

[Nitemare]

Finally something I can answer somewhat intelligently :-}

Typically RAID-6 is used with SATA drives, you have SAS, which are more reliable, so save the extra drive.

If you are doing high i/o, then put as many drives into one volume as you can, more drives mean higher i/o. Less drives means less i/o.

I would carve 1 RAID volume set, ie RAID-10 or RAID-5, across maximum drives, then carve out our luns/volumes as you need them. That way your data stripes are across the maximum amount of drives while the individual luns/vols are what you need.

My best advice, experiement, see if you notice a performance difference.

Cheers

[Nitemare]

And learn from my spelling mistakes as well :-}

experiement should be "experiment"

Cheers,

N

[George_B]

I have decided to try and amend the order for the server before it is built to replace two of the 146GB drives with 73GB 15K RPM drives.

I will then go for RAID 10 with the two 15K drives and a RAID 5 array with 5 disks and one hot swap spare. ESX OS and swap will go on the RAID 10 array and the VMFS on the RAID 5.

[wood175]

"I will then go for RAID 10 with the two 15K drives and a RAID 5 array with 5 disks and one hot swap spare."

This is an old post, but performance to dollar, (2) 75GB 15k SAS - ESXi Install (6) 146/300 15k SAS in RAID 1 + 0

Always works well for me, and when in a Virtual atmosphere, I generally buy refurb drives, and keep two extras, saves money- not much risk.