[Gluster-users] Access data directly from underlying storage

[Melkor Lord]

On Wed, Mar 18, 2015 at 6:22 PM, Rumen Telbizov <telbizov at gmail.com> wrote:

>
>
> *Can I directly access the data on the underlying storage volumes?*
>>
>> If you are just doing just read()/access()/stat() like operations, you
>> should be fine. If you are not using any new features (like
>> quota/geo-replication etc etc) then technically, you can modify (but surely
>> not rename(2) and link(2)) the data inside.
>>
>> Note that this is not tested as part of gluster’s release cycle and not
>> recommended for production use.
>>
>
> The last sentence doesn't recommend it for production use. I was wondering
> if there's any other concern besides the fact that it's not tested as part
> of the release cycle or one could expect actual some problems with the data
> being read while doing so?
>
> What I am interested is *only* read operations (readdir, stat, read
> data). All the write operations will continue going over the shared/mounted
> drive. So what I want to know is that the data that I am reading will be
> consistent with the rest of the bricks and not corrupted in any way.
>

This is not necessarily a direct answer to your question but I've tested
something similar. With a running volume (but not mounted anywhere), I
copied a file directly to the underlying FS directory (a tarball) to test
how it would react if a client would mount the volume afterwards.

When a client mounted the Gluster filesystem (FUSE client), after some
time, the tarball I copied on one of the bricks was replicated to the other
servers in my 3 replica test environment.

I tested the tarball on each gluster server and it was perfectly consistent.

During all my other tests, I did things like the one you intend to do.
Mounted the gluster volume on a client and copied some big files there.
While the copy was doing its job, I directly accessed the resulting file on
the servers to see if it was consistent (checking the first few KB of the
file to check headers)

I haven't found anything to complain about and all seemed consistent to me
so I'd say that what you plan to do is fairly safe.



-- 
Unix _IS_ user friendly, it's just selective about who its friends are.
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