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Re: sizing log - is there a too big?

To: aurfalien <aurfalien@xxxxxxxxx>
Subject: Re: sizing log - is there a too big?
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Fri, 28 Jun 2013 11:56:10 +1000
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <73A9FC1C-854D-4C23-B560-FEEF64A3001B@xxxxxxxxx>
References: <55C24454-59E9-4285-9A4C-C4BD24EDBEEC@xxxxxxxxx> <20130627014810.GA29790@dastard> <73A9FC1C-854D-4C23-B560-FEEF64A3001B@xxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Thu, Jun 27, 2013 at 08:58:06AM -0700, aurfalien wrote:
> 
> On Jun 26, 2013, at 6:48 PM, Dave Chinner wrote:
> 
> > On Wed, Jun 26, 2013 at 04:56:31PM -0700, aurfalien wrote:
> >> Hi all,
> >> 
> >> Wondering if my log being just under 2GB is a bad idea.
> >> 
> >> Noticing flush-253:2/kcopyd which is my XFS file system getting
> >> really high load avg and wait times via top).
> > 
> > What has the log size got to do with something that is happening at
> > the block layer? What's your storage config?
> > 
> >> Doing a simple rsync over NFS and after a bit, the system gets to a load 
> >> of 24.... yikes...
> > 
> > Let me guess - 24 nfsds blocked waiting for kcopyd to do it's stuff?
> > 
> > Load average going up when the NFS server is busy generally means
> > your IO subsystem is heavily loaded - it's not uncommon to see large
> > NFS servers that are extremely busy sustain load averages over a
> > 100 (or even 1000) for hours/days on end....
> > 
> >> Upon killing the rsync, I am seeing loads going down to sub 1
> >> after about 10 min.  I have repeated this to verify 10 min.
> > 
> > Sure. Processes blocked on IO contribute to the load average. Kill
> > the IO load, and the load average will return to nothing in 10-15
> > minutes.
> 
> 
> Not so fast my fine feathered friend.
> 
> Same work load, same hardware.
> 
> Only diff is;
> 
> External log, its 2GB
> And its Centos 6.4 which was previously 5.9.

Oh, you're comparing behaviour between kernels 5 years in age
difference. Well, things change, and a change of load average for
the same workload between very different kernels is no unexpected.

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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