netapp  had recommended to us a rg size of 16 with raid_dp,  will we get better performance out of a 22-25 disk rg or is that for specific applications?


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Daniel Leeds
Senior Systems Administrator
Edmunds.com



-----Original Message-----
From: owner-toasters@mathworks.com on behalf of Nils Vogels
Sent: Sat 3/17/2007 3:10 PM
To: Darish Rajanayagam
Cc: toasters@mathworks.com
Subject: Re: FAS3020 - aggr best practises.

Hey Darish,

On 3/17/07, Darish Rajanayagam <darishr@softcom.biz> wrote:
>
> The current configuration is one large RAID DP Group with 1 HotSpare (27
> Disk DP RAID Group), which belong to one aggregate (aggr0).
>
> My question:
>
> The new enclosures, should I create 2 x 28 Disk DP RAID groups and add it to
> the existing aggregate? The application we run is IO intensive and more
> spindles the better. Does anyone see any disadvantages of doing the above?

The performance of a raidgroup depends on the number of spindles in
the raidgroup, and in my experience not on the amount of rg's in an
aggr. In my experience, the most applications perform best with about
22 - 25 disks / rg, after that the performance doesn't seem to
increase that much anymore.

If you need to serve the data out of one volume
(mountpoint/share/lun), you have no option but to expand your aggr,
and in general that is something that works best. You can create more
aggregates however, this gives you more future flexibility since you
cannot destroy raidgroups, but only whole aggregates.

> Does anyone have a formula to calculate mean time to Repair on the 10K 144GB
> disks on a busy filer? I only have one hot spare disk, should I add more, is
> there a rule of thumb?

I generally use one hotspare per set of 40-60 disks, depending on the
need for redundancy. With DP on FC you are reasonably safe, so I'd opt
of 1 spare per 60 disks and round that number up.

I have seen reconstruct times of roughly 3-4h for a 10K 144GB disk,
this offcourse depends a lot on the load of your box. You can always
tune the reconstruct priorities. Also, don't forget you have RAID-DP
so you are protected against double-disk failure within a raidgroup.

> We currently have multiple volumes on the filer, after adding the new
> shelves/spindles, if I run a reallocate  on the existing volumes, would it
> take advantage of the additional spindles.

Only if you expanded the aggregate where the volume resides in. And
yes, if remotely possibly, try to reallocate if you grow a busy
aggregate. You can also schedule regular reallocate jobs using the
"reallocate schedule" command, which IIRC appeared in 7.0.5.

A scheduled reallocation job will first scan if the reallocation is
needed and only then fire off a wafl reallocate.

Gr,

Nils

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