[Gluster-devel] Parallel readdir from NFS clients causes incorrect data

Anand Avati anand.avati at gmail.com
Wed Apr 3 23:35:32 UTC 2013

Hmm, I was be tempted to suggest that you were bitten by the gluster/ext4
readdir's d_off incompatibility issue (which got recently fixed
http://review.gluster.org/4711/). But you say it works fine when you do ls
one at a time sequentially.

I just realized after reading your email that, in glusterfs, because we use
the same anonymous fd for multiple client/application's readdir query, we
have a race in the posix translator where two threads attempt to push/pull
the same backend cursor in a chaotic way resulting in duplicate/lost
entries. This might be the issue you are seeing, just guessing.

Will you be willing to try out a source cod patch on top of the git HEAD to
rebuild your glusterfs and verify if it fixes the issue? Will really
appreciate it!


On Wed, Apr 3, 2013 at 2:37 PM, Michael Brown <michael at netdirect.ca> wrote:

>  I'm seeing a problem on my fairly fresh RHEL gluster install. Smells to
> me like a parallelism problem on the server.
> If I mount a gluster volume via NFS (using glusterd's internal NFS server,
> nfs-kernel-server) and read a directory from multiple clients *in
> parallel*, I get inconsistent results across servers. Some files are
> missing from the directory listing, some may be present twice!
> Exactly which files (or directories!) are missing/duplicated varies each
> time. But I can very consistently reproduce the behaviour.
> You can see a screenshot here: http://imgur.com/JU8AFrt
> The replication steps are:
> * clusterssh to each NFS client
> * unmount /gv0 (to clear cache)
> * mount /gv0 [1]
> * ls -al /gv0/common/apache-jmeter-2.9/bin (which is where I first
> noticed this)
> Here's the rub: if, instead of doing the 'ls' in parallel, I do it in
> series, it works just fine (consistent correct results everywhere). But
> hitting the gluster server from multiple clients *at the same time*causes problems.
> I can still stat() and open() the files missing from the directory
> listing, they just don't show up in an enumeration.
> Mounting gv0 as a gluster client filesystem works just fine.
> Details of my setup:
> 2 × gluster servers: 2×E5-2670, 128GB RAM, RHEL 6.4 64-bit,
> glusterfs-server-3.3.1-1.el6.x86_64 (from EPEL)
> 4 × NFS clients: 2×E5-2660, 128GB RAM, RHEL 5.7 64-bit,
> glusterfs-3.3.1-11.el5 (from kkeithley's repo, only used for testing)
> gv0 volume information is below
> bricks are 400GB SSDs with ext4[2]
> common network is 10GbE, replication between servers happens over direct
> 10GbE link.
> I will be testing on xfs/btrfs/zfs eventually, but for now I'm on ext4.
> Also attached is my chatlog from asking about this in #gluster
> [1]: fstab line is: fearless1:/gv0 /gv0 nfs
> defaults,sync,tcp,wsize=8192,rsize=8192 0 0
> [2]: yes, I've turned off dir_index to avoid That Bug. I've run the d_off
> test, results are here: http://pastebin.com/zQt5gZnZ
> ----
> gluster> volume info gv0
> Volume Name: gv0
> Type: Distributed-Replicate
> Volume ID: 20117b48-7f88-4f16-9490-a0349afacf71
> Status: Started
> Number of Bricks: 8 x 2 = 16
> Transport-type: tcp
> Bricks:
> Brick1: fearless1:/export/bricks/500117310007a6d8/glusterdata
> Brick2: fearless2:/export/bricks/500117310007a674/glusterdata
> Brick3: fearless1:/export/bricks/500117310007a714/glusterdata
> Brick4: fearless2:/export/bricks/500117310007a684/glusterdata
> Brick5: fearless1:/export/bricks/500117310007a7dc/glusterdata
> Brick6: fearless2:/export/bricks/500117310007a694/glusterdata
> Brick7: fearless1:/export/bricks/500117310007a7e4/glusterdata
> Brick8: fearless2:/export/bricks/500117310007a720/glusterdata
> Brick9: fearless1:/export/bricks/500117310007a7ec/glusterdata
> Brick10: fearless2:/export/bricks/500117310007a74c/glusterdata
> Brick11: fearless1:/export/bricks/500117310007a838/glusterdata
> Brick12: fearless2:/export/bricks/500117310007a814/glusterdata
> Brick13: fearless1:/export/bricks/500117310007a850/glusterdata
> Brick14: fearless2:/export/bricks/500117310007a84c/glusterdata
> Brick15: fearless1:/export/bricks/500117310007a858/glusterdata
> Brick16: fearless2:/export/bricks/500117310007a8f8/glusterdata
> Options Reconfigured:
> diagnostics.count-fop-hits: on
> diagnostics.latency-measurement: on
> nfs.disable: off
> ----
> --
> Michael Brown               | `One of the main causes of the fall of
> Systems Consultant          | the Roman Empire was that, lacking zero,
> Net Direct Inc.             | they had no way to indicate successful
> ☎: +1 519 883 1172 x5106    | termination of their C programs.' - Firth
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