Re: storage controllers for use with NFS+BtrFs

[Benjamin Coddington <bcodding@redhat.com>]

Hi Daniel,

On Mon, 19 Jan 2015, Daniel Pocock wrote:
> I've been looking into the issue of which storage controllers are
> suitable for use with NFS + BtrFs (or NFS + ZFS) and put some comments
> about it on my blog[1] today.
>
> I understand that for NFS it is generally desirable to have non-volatile
> write cache if you want good write performance.
>
> On the other hand, self-healing file systems (BtrFs and ZFS) like having
> direct access to disks and those RAID cards with caches don't always
> give the same level of access to the volume.
>
> Can anybody give any practical suggestions about how to reconcile these
> requirements and experience good NFS write performance onto these
> filesystems given the type of HBA and RAID cards available?

I don't think that reconciling these requirements is going to necessarily
equal good NFS write performance.  You've got to define what good means.
It sounds like you want fast commits, but how fast, how many, what size?

If you're building on ZFS, best thing would be to find a very fast ZIL
device, but if you're already building pools on SSD to get any gain you'd
need something really fast like DDR.  A ramdrive ZIL might be a nice way to
test that on your setup before spending anything.

Many BBU-d RAID controllers allow JBOD modes that still slice up their
cache for writes to disk, for example check out megacli's
"-CfgEachDskRaid0".

Ben

>
> 1. http://danielpocock.com/storage-controllers-for-small-linux-nfs-networks
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