[CentOS] Is glusterfs ready?

Jose P. Espinal jose at pavelespinal.com
Tue Sep 11 11:45:46 EDT 2012


On Wed, Sep 5, 2012 at 12:00 PM, John Doe <jdmls at yahoo.com> wrote:

> From: Dennis Jacobfeuerborn <dennisml at conversis.de>
>
> >On 09/05/2012 07:14 AM, Bob Hepple wrote:
> >> Another factor is that the available space is the physical space
> >> divided by 4 due to the replication across the nodes on top of the
> >> nodes being RAID'd themselves.
> >That really depends on your setup. I'm not sure what you mean by the nodes
> >being raided themselves.
> I think he meant gluster "RAID1" plus hardware RAID (10 I guess from the
> x2, instead of standalone disks).
>
> JD
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Hello, this comment was posted on a site I administer, where
I chronologically publish an archive of some CentOS (and some other
distros) lists:

===== [comment] =====
A new comment on the post "Is Glusterfs Ready?"

Author : Jeff Darcy (IP: 173.48.139.36 ,
pool-173-48-139-36.bstnma.fios.verizon.net)
E-mail : jeff at pl.atyp.us
URL    : http://pl.atyp.us
Whois  : http://whois.arin.net/rest/ip/173.48.139.36
Comment:

Hi.  I'm one of the GlusterFS developers, and I'll try to offer a slightly
different perspective.

First, sure GlusterFS has bugs.  Some of them even make me cringe.  If we
really wanted to get into a discussion of the things about GlusterFS that
suck, I'd probably be able to come up with more things than anybody, but
one of the lessons I learned early in my career is that seeing all of the
bugs for a piece of software leads to a skewed perspective.  Some people
have had problems with GlusterFS but some people have been very happy with
it, and I guarantee that every alternative has its own horror stories.
 GlusterFS and XtreemFS were the only two distributed filesystems that
passed some *very simple* tests I ran last year.  Ceph crashed.  MooseFS
hung (and also doesn't honor O_SYNC).  OrangeFS corrupted data.  HDFS
cheats by buffering writes locally, and doesn't even try to implement half
of the required behaviors for a general-purpose filesystem.  I can go
through any of those codebases and find awful bug after horrible bug after
data-destroying bug . . . and yet each of them has their fans too, because
most users could never possibly hit the edge conditions where those bugs
exist.  The lesson is that anecdotes do not equal data.  Don't listen to
vendor hype, and don't listen to anti-vendor bashing either.  Find out what
the *typical* experience across a large number of users is, and how well
the software works in your own testing.

Second, just as every piece of software has bugs, every truly distributed
filesystem (i.e. not NFS) struggles with lots of small files.  There has
been some progress in this area with projects like Pomegranate and GIGA+,
we have some ideas for how to approach it in GlusterFS (see my talk at SDC
next week), but overall I think it's important to realize that such a
workload is likely to be problematic for *any* offering in the category.
 You'll have to do a lot of tuning, maybe implement some special
workarounds yourself, but if you want to combine this I/O profile with the
benefits of scalable storage it can all be worth it.

Lastly, if anybody is paying a 4x disk-space penalty (at one site) I'd say
they're overdoing things.  Once you have replication between servers,
RAID-1 on each server is overkill.  I'd say even RAID-6 is overkill.  How
many simultaneous disk failures do you need to survive?  If the answer is
two, as it usually seems to be, then GlusterFS replication on top of RAID-5
is a fine solution and requires a maximum of 3x (more typically just a bit
more than 2x).  In the future we're looking at various forms of compression
and deduplication and erasure codes that will all bring the multiple down
even further.

So I can't say whether it's ready or whether you can trust it.  I'm not
objective enough for my opinion on that to count for much.  What I'm saying
is that distributed filesystems are complex pieces of sofware, none of the
alternatives are where any of us working on them would  like to be, and the
only way any of these projects get better is if users let us know of
problems they encounter.  Blog posts or comments describing specific
issues, from people whose names appear nowhere on any email or bug report
the developers could have seen, don't help to advance the state of the art.

===== [/comment] =====


Regards,


-- 
J. Pavel Espinal
Skype: p.espinal
http://ww.pavelespinal.com
http://www.slackware-es.com


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