[Gluster-users] Sharding on 7.x - file sizes are wrong after a large copy.

[Claus Jeppesen]

In April of this year I reported the problem using sharding on gluster 7.4:

====
We're using GlusterFS in a replicated brick setup with 2 bricks with
sharding turned on (shardsize 128MB).

There is something funny going on as we can see that if we copy large VM
files to the volume we can end up with files that are a bit larger than the
source files DEPENDING on the speed with which we copied the files - e.g.:

   dd if=SOURCE bs=1M | pv -L NNm | ssh gluster_server "dd
of=/gluster/VOL_NAME/TARGET
bs=1M"

It seems that if NN is <= 25 (i.e. 25 MB/s) the size of SOURCE and TARGET
will be the same.

If we crank NN to, say, 50 we sometimes risk that a 25G file ends up having
a slightly larger size, e.g. 26844413952 or 26844233728 - larger than the
expected 26843545600.
Unfortunately this is not an illusion ! If we dd the files out of Gluster
we will receive the amount of data that 'ls' showed us.

In the brick directory (incl .shard directory) we have the expected amount
of shards for a 25G files (200) with size precisely equal to 128MB - but
there is an additional 0 size shard file created.

Has anyone else seen a phenomenon like this ?
====

After upgrade to 7.6 we're still seeing this problem - now,  the extra
bytes that are appearing can be removed using truncate in the mounted
gluster volume, and md5sum can confirm that after truncate the content is
identical to the source - however, it may point to an underlying issue.

I hope someone can reproduce this behaviour,

Thanx,

Claus.

-- 
*Claus Jeppesen*
Manager, Network Services
Datto, Inc.
p +45 6170 5901 | Copenhagen Office
www.datto.com
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