[Gluster-users] 3.7.16 with sharding corrupts VMDK files when adding and removing bricks
gandalf.corvotempesta at gmail.com
Mon Nov 14 16:29:00 UTC 2016
1016-11-14 17:01 GMT+01:00 Vijay Bellur <vbellur at redhat.com>:
> Accessing sharded data after disabling sharding is something that we
> did not visualize as a valid use case at any point in time. Also, you
> could access the contents by enabling sharding again. Given these
> factors I think this particular problem has not been prioritized by
That's not true.
If you have VMs running on a sharded volume and you disable sharding,
with the VM still running, everything crash and could lead to data loss, as VM
will be unable to find their filesystem and so on, qemu currupts the
image and so on.....
If I write to a file that was shareded, (in example a log file), now
when you disable the shard,
the application would write the existing file (the one that was the
If you reenable sharding, you lost some data
128MB file. shard set to 64MB. You have 2 chunks: shard1+shard2
Now you are writing to the file:
AAAA+BBBB are placed on shard1, CCCC+DDDD are placed on shard2
If you disable the shard and write some extra data, EEEE, then EEEE
would be placed after BBBB in shard1 (growing more than 64MB)
and not on shard3
If you re-enable shard, EEEE is lost, as gluster would expect it as
shard3. and I think gluster will read only the first 64MB from shard1.
If gluster read the whole file, you'll get something like this:
in a text file this is bad, in a VM image, this mean data
loss/corruption almost impossible to fix.
> As with many other projects, we are in a stage today where the number
> of users and testers far outweigh the number of developers
> contributing code. With this state it becomes hard to prioritize
> problems from a long todo list for developers. If valuable community
> members like you feel strongly about a bug or feature that need
> attention of developers, please call such issues out on the mailing
> list. We will be more than happy to help.
That's why i've asked for less feature and more stability.
If you have to prioritize, please choose all bugs that could lead to
data corruption or similiar.
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