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Suggestion required on creating vg with 800gb

 
Venkat Nagesh
Occasional Contributor

Suggestion required on creating vg with 800gb

Hi,

I need to create a VG with 800GB Single SAN Disk. I would be creating 13 LV's in that and few of the LV's are of 300GB,150GB size.

Let me know whether using single SAN disk for this is recommended or not?(Because EVA 5000 doesnot support more than 512 vdisks and we need to migrate the data from multiple vdisks to single one due to this limitation).
If it is OK to create a VG with single 800gb disk then let me know which is the best suited PE Size for this. These filesystems would contain clearcase Vobs data and no database.OS is 11.00
2 REPLIES 2
A. Clay Stephenson
Acclaimed Contributor

Re: Suggestion required on creating vg with 800gb

You can do this but almost certainly you are going to see some performance impact; not directly from the number of disks that comprise this VG but rather because of the reduced number of i/o paths. The whole idea is to get the data from the host to the array as quickly as possible and let the array decide what to do with it --- that's what them expensive arrays is good at. Rather than paring down your VG to a single LUN (vdisk), I would break the VG into as many PV as you have separate i/o paths for. Oh, and don't be fooled by the bandwidth of a Fibre controller; very seldom will you see real transfer rates approaching those values -- so the more separate i/o channels the better.

In your 800GB example, I assume that you have 4 Fibre-channel connects. Rather than 1 800GB LUN, I would create 4 200GB LUN's: LUN0 would use SCSI path A, alternate B; LUN1 would use SCSI path B, alternate C;
LUN2 would use SCSI path C, alternate D;
LUN3 would use SCSI path D, alternate A.

Now each LVOL in this VG would be stripped across all 4 LUN's typically in 64-128KB chunks. This will give you the highest possible throughput and efficiently spread the i/o.

You question about extent size is pointless. The smallest possible PE size (1MB) is still too large to spread the i/o well and 1MB PE's would severely limit the size of each PV.
If it ain't broke, I can fix that.
Alzhy
Honored Contributor

Re: Suggestion required on creating vg with 800gb

1 large 800GB LUN presented by default to 2 active FC Paths (1 Controller) or 4 200GB LUNs path preferred alternating between the 2 HSV controllers and stiped?

In my testing via IOZONE - no difference in performance. That 800GB LUN is already optimal and it's already using (or has the potential) to use the bandwidth on your FC paths... Sorry A. CLay but I too had that initial plan but the EVA5K is just so auto-everything -- nothing more that can be done to take the most out of it.

My preference (since this is an EVA5K) is to simply use that single 800GB LUN/vdisk and chop/carve it up into individual lvols (if LVM) or vols (if VxVM)...

Hakuna Matata.