[Gluster-users] Very slow directory listing and high CPU usage on replicated volume
landman at scalableinformatics.com
Mon Nov 5 15:06:43 UTC 2012
On 11/05/2012 09:57 AM, harry mangalam wrote:
> Jeff Darcy wrote a nice piece in his hekafs blog about 'the importance of
> keeping things sequential' which is essentially about the contention for heads
> between data io and journal io.
> (also congrats on the Linux Journal article on the glupy python/gluster
> We've been experimenting with SSDs on ZFS (using the SSDs fo the ZIL
> (journal)) and while it's provided a little bit of a boost, it has not been
> dramatic. Ditto XFS. However, we did not stress it at all with heavy loads
An issue you have to worry about is if the SSD streaming read/write path
is around the same speed as the spinning rust performance. If so, this
design would be a wash at best.
Also, if this is under Linux, the ZFS pathways may not be terribly well
> in a gluster env and I'm now thinking that there is where you would see the
> improvement. (see Jeff's graph about how the diff in threads/load affects
> Is anyone running a gluster system with the underlying XFS writing the journal
> to SSDs? If so, any improvement? I would have expected to hear about this as
> a recommended architecture for gluster if it had performed MUCH better, but
Yes, we've done this, and do this on occasion. No, there's no dramatic
speed boost for most use cases.
Unfortunately, heavy metadata ops on GlusterFS are going to be slow, and
we simply have to accept that for the near term. This appears to be
independent of the particular file system, or even storage technology.
If you aren't doing metadata heavy ops, then you should be in good
shape. It appears that mirroring magnifies the metadata heavy ops
For laughs, about a year ago, we set up large ram disks (tmpfs) in a
cluster, put a loopback device on them, then a file system, then
GlusterFS atop this. Should have been very fast for metadata ops. But
it wasn't. Gave some improvement, but not significant enough that we'd
recommend doing "heroic" designs like this.
If your workloads are metadata heavy, we'd recommend local IO, and if
you are mostly small IO, an SSD.
Joseph Landman, Ph.D
Founder and CEO
Scalable Informatics, Inc.
email: landman at scalableinformatics.com
web : http://scalableinformatics.com
phone: +1 734 786 8423 x121
cell : +1 734 612 4615
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