[Gluster-users] Gluster-users Digest, Vol 20, Issue 22

Liam Slusser lslusser at gmail.com
Tue Jan 5 18:00:59 UTC 2010

Larry & All,

I would much rather rebuild a bad drive with a raid controller then
have to wait for Gluster to do it.  With a large number of files doing
a ls -aglR can take weeks.  Also you don't NEED enterprise drives with
a raid controller, i use desktop 1.5tb Seagate drives which happy as a
clam on a 3ware SAS card under a SAS expander.


On Thu, Dec 17, 2009 at 8:17 AM, Larry Bates <larry.bates at vitalesafe.com> wrote:
> Phi.l,
> I think the real question you need to ask has to do with why we are using
> GlusterFS at all and what happens when something fails.  Normally GlusterFS
> is used to provide scalability, redundancy/recovery, and performance.  For
> many applications performance will be the least of the worries so we
> concentrate on scalability and redundancy/recovery.  Scalability can be
> achieved no matter which way you configure your servers.  Using distribute
> translator (DHT) you can unify all the servers into a single virtual storage
> space.  The problem comes when you look at what happens when you have a
> machine/drive failures and need the redundancy/recovery capabilities of
> GlusterFS.  By putting 36Tb of storage on a single server and exposing it as
> a single volume (using either hardware or software RAID), you will have to
> replicate that to a replacement server after a failure.  Replicating 36Tb
> will take a lot of time and CPU cycles.  If you keep things simple (JBOD)
> and use AFR to replicate drives between servers and use DHT to unify
> everything together, now you only have to move 1.5Tb/2Tb when a drive fails.
>  You will also note that you get to use 100% of your disk storage this way
> instead of wasting 1 drive per array with RAID5 or two drives with RAID6.
>  Normally with RAID5/6 it is also imperative that you have a hot spare per
> array, which means you waste an additional driver per array.  To make
> RAID5/6 work with no single point of failure you have to do something like
> RAID50/60 across two controllers which gets expensive and much more
> difficult to manage and to grow.  Implementing GlusterFS using more modest
> hardware makes all those "issues" go away.  Just use GlusterFS to provide
> the RAID-like capabilities (via AFR and DHT).
> Personally I doubt that I would set up my storage the way you describe.  I
> probably would (and have) set it up with more smaller servers.  Something
> like three times as many 2U servers with 8x2Tb drives each (or even 6 times
> as many 1U servers with 4x2Tb drives each) and forget the expensive RAID
> SATA controllers, they aren't necessary and are just a single point of
> failure that you can eliminate.  In addition you will enjoy significant
> performance improvements because you have:
> 1) Many parallel paths to storage (36x1U or 18x2U vs 6x5U servers).  Gigabit
> Ethernet is fast, but still will limit bandwidth to a single machine.
> 2) Write performance on RAID5/6 is never going to be as fast as JBOD.
> 3) You should have much more memory caching available (36x8Gb = 256Gb memory
> or 18x8Gb memory = 128Gb vs maybe 6x16Gb = 96Gb)
> 4) Management of the storage is done in one place..GlusterFS.  No messy RAID
> controller setups to document/remember.
> 5) You can expand in the future in a much more granular and controlled
> fashion.  Add 2 machines (1 for replication) and you get 8Tb (using 2Tb
> drives) of storage.  When you want to replace a machine, just set up new
> one, fail the old one, and let GlusterFS build the new one for you (AFR will
> do the heavy lifting).  CPUs will get faster, hard drives will get faster
> and bigger in the future, so make it easy to upgrade.  A small number of BIG
> machines makes it a lot harder to do upgrades as new hardware becomes
> available.
> 6) Machine failures (motherboard, power supply, etc.) will effect much less
> of your storage network.  Having a spare 1U machine around as a hot spare
> doesn't cost much (maybe $1200).  Having a spare 5U monster around does
> (probably close to $6000).
> IMHO 36 x 1U or 18 x 2U servers shouldn't cost any more (and maybe less)
> than the big boxes you are looking to buy.  They are commodity items.  If
> you go the 1U route you don't need anything but a machine, with memory and 4
> hard drives (all server motherboards come with at least 4 SATA ports).  By
> using 2Tb drives, I think you would find that the cost would be actually
> less.  By NOT using hardware RAID you can also NOT use RAID-class hard
> drives which cost about $100 each more than non-RAID hard drives.  Just that
> change alone could save you 6 x 24 = 144 x $100 = $14,400!  JBOD just
> doesn't need RAID-class hard drives because you don't need the sophisticated
> firmware that the RAID-class hard drives provide.  You still will want
> quality hard drives, but failures will have such a low impact that it is
> much less of a problem.
> By using more smaller machines you also eliminate the need for redundant
> power supplies (which would be a requirement in your large boxes because it
> would be a single point of failure on a large percentage of your storage
> system).
> Hope the information helps.
> Regards,
> Larry Bates
> ------------------------------
>> Message: 6
>> Date: Thu, 17 Dec 2009 00:18:54 -0600
>> From: phil cryer <phil at cryer.us>
>> Subject: [Gluster-users] Recommended GlusterFS configuration for 6
>>        node    cluster
>> To: "gluster-users at gluster.org" <gluster-users at gluster.org>
>> Message-ID:
>>        <3a3bc55a0912162218i4e3f326cr9956dd37132bfc19 at mail.gmail.com>
>> Content-Type: text/plain; charset=UTF-8
>> We're setting up 6 servers, each with 24 x 1.5TB drives, the systems
>> will run Debian testing and Gluster 3.x.  The SATA RAID card offers
>> RAID5 and RAID6, we're wondering what the optimum setup would be for
>> this configuration.  Do we RAID5 the disks, and have GlusterFS use
>> them that way, or do we keep them all 'raw' and have GlusterFS handle
>> the replication (though not 2x as we would have with the RAID
>> options)?  Obviously a lot of ways to do this, just wondering what
>> GlusterFS devs and other experienced users would recommend.
>> Thanks
>> P
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