Re: posix_fallocate

["Krzysztof Błaszkowski" <kb@sysmikro.com.pl>]

On Friday 07 May 2010 11:23, Stan Hoeppner wrote:
> Krzysztof Błaszkowski put forth on 5/7/2010 3:22 AM:
> > Hello,
> >
> > I use this to preallocate large space but found an issue. Posix_fallocate
> > works right with sizes like 100G, 1T and even 10T on some boxes (on some
> > other can fail after e.g. 7T threshold) but if i tried e.g. 16T the user
> > space process would be "R"unning forever and it is not interruptible.
> > Furthermore some other not related processes like sshd, bash enter D
> > state. There is nothing in kernel log.
> >
> > I made so far a few logs with ftrace facility for 1G, 100G, 1T and 10T
> > sizes. I noticed that for 1st three sizes the log is as long as abt 1.5M
> > (2M peak) while 10T generates 94M long log. I couldn't retrieve a log for
> > 17T case because "cat /sys ... /trace" enters D.
> >
> > I would appreciate any help because i gave up with ftrace logs analysis.
> > The xfs_vn_fallocate is covered in abt 11k lines for a 1.5M log case
> > while there are abt 163k lines in 94M log. And all i could see is poss
> > some relationship between time spent in xfs_vn_fallocate subfunctions vs
> > requested space.
> >
> > Box details:
> > 16 Hitachi 2TB drives (backplane connected), dm, 1 lvm lun of 25T size,
> > kernel 2.6.31.5, more recent kernels neither xfs were not tested.
>
> 32 or 64 bit kernel? 

sorry, i meant 64 bit.

> What is the size of the XFS filesystem on the 25TB 
> LVM LUN against which you're running posix_fallocate?

xfs occupies whole lun (ie 25TB)

> The reason I ask is 
> that XFS has a 16TB per filesystem limitation on 32 bit kernels.  I can
> only assume that your XFS filesystem is larger than 16TB since you're
> attempting to posix_fallocate 16TB.  But, it's best to ask for confirmation
> rather than assume, especially given that your problem is appearing near
> that magical 16TB boundary.

sure, i see. I use 64 bit by default.

Regards,
Krzysztof

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