[Gluster-users] [SPAM?] Non-uniform backend brick sizes

Dan Bretherton d.a.bretherton at reading.ac.uk
Wed May 4 12:43:34 UTC 2011

Hi James, thanks for your suggestions.   I have used the rebalance 
command several times after adding new bricks, and I am pretty sure that 
it equalizes the amount of data stored on each brick rather than the 
amount of free space.  It would be useful to have an option to equalize 
free space instead - that would certainly solve the problem of 
non-uniform brick sizes.

There used to be a server vol file option "min-free-disk", to leave 
space on bricks for files to grow.  That would solve my problem as 
well.  Do you know if this is available in 3.1.x or 3.2, or if there is 
a CLI command for setting it?


On 02/05/11 13:11, Burnash, James wrote:
> Hi Dan.
> I believe that you would have to run this command:
> gluster volume rebalance <volname> start
> at which point, Gluster will try to balance the files amongst the 
> storage nodes. Whether or not it will accommodate non-uniform bricks I 
> don't know for sure (since mine are uniform), but I believe that it 
> will look at actual space available and try to make intelligent 
> decisions on where to place files.
> Please check with the devs before implementing my suggestion, however 
> -- don't want to cause any harm since I'm unsure.
> James Burnash, Unix Engineering
> *From:*gluster-users-bounces at gluster.org 
> [mailto:gluster-users-bounces at gluster.org] *On Behalf Of *Dan Bretherton
> *Sent:* Sunday, May 01, 2011 9:01 AM
> *To:* gluster-users
> *Subject:* [SPAM?] [Gluster-users] Non-uniform backend brick sizes
> *Importance:* Low
> Hello All-
> After posting to a previous thread about this issue 
> (http://gluster.org/pipermail/gluster-users/2011-April/007157.html) I 
> decided to start a new thread, mainly because I think I have found a 
> problem relating to this setup.  Our servers vary in size quite a lot, 
> so some of the bricks in one particular volume are 100% full.  This 
> has not caused us any problems until now, because new files are always 
> created on larger bricks where there is still space.  However, 
> yesterday a user complained that he was getting "device full" errors 
> even though df reported several hundred GB free in the volume.  The 
> problem turned out to be caused by over-writing pre-existing files 
> that were stored on one or more full bricks.  Deleting the old files 
> before creating them again cured the problem, because the new files 
> were then created on larger bricks.  Is this a known problem when 
> using distributed or distributed/replicated volumes with non uniform 
> backend sizes, and is there any way to avoid it?
> Lifting some comments and questions from the other thread...
> From this posting: 
> http://gluster.org/pipermail/gluster-users/2011-March/007103.html
> >  I see that
> >  your backend sizes are different... Its preferred  to keep them uniform.
> And from this posting: 
> http://gluster.org/pipermail/gluster-users/2011-March/007104.html
> >  try to keep the backend uniform to avoid any possible issues which may
> >  arise later.
> Please could someone comment on the "possible issues that might arise" 
> with with a setup involving non-uniform backend brick sizes.  All 
> comments and suggestions would be much appreciated.
> -Dan.
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