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From: Brian Candler <B.Candler@pobox.com>
To: Stan Hoeppner <stan@hardwarefreak.com>
Cc: Christoph Hellwig <hch@infradead.org>, xfs@oss.sgi.com
Subject: Re: Performance problem - reads slower than writes
Date: Sun, 5 Feb 2012 09:05:02 +0000	[thread overview]
Message-ID: <20120205090502.GA3961@nsrc.org> (raw)
In-Reply-To: <4F2E10C1.3040200@hardwarefreak.com>

On Sat, Feb 04, 2012 at 11:16:49PM -0600, Stan Hoeppner wrote:
> When you lose a disk in this setup, how do you rebuild the replacement
> drive?  Do you simply format it and then move 3TB of data across GbE
> from other Gluster nodes?

Basically, yes. When you read a file, it causes the mirror to synchronise
that particular file. To force the whole brick to come back into sync you
run find+stat across the whole filesystem.
http://download.gluster.com/pub/gluster/glusterfs/3.2/Documentation/AG/html/sect-Administration_Guide-Managing_Volumes-Self_heal.html

> Even if the disk is only 1/3rd full, such a
> restore seems like an expensive and time consuming operation.  I'm
> thinking RAID has a significant advantage here.

Well, if you lose a 3TB disk in a RAID-1 type setup, then the whole disk has
to be copied block by block (whether it contains data or not). So the
consideration here is network bandwidth.

I am building with 10GE, but even 1G would be just about sufficient to carry
the peak bandwidth of a single one of these disks.  (dd on the raw disk
gives 120MB/s at the start and 60MB/s at the end)

The whole manageability aspect certainly needs to be considered very
seriously though.  With RAID1 or RAID10, dealing with a failed disk is
pretty much pull and plug; with Gluster we'd be looking at having to mkfs
the new filesystem, mount it at the right place, and then run the self-heal. 
This will have to be weighed against the availability advantages of being
able to take an entire storage node out of service.

Regards,

Brian.

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  reply	other threads:[~2012-02-05  9:05 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-01-30 22:00 Performance problem - reads slower than writes Brian Candler
2012-01-31  2:05 ` Dave Chinner
2012-01-31 10:31   ` Brian Candler
2012-01-31 14:16     ` Brian Candler
2012-01-31 20:25       ` Dave Chinner
2012-02-01  7:29         ` Stan Hoeppner
2012-02-03 18:47         ` Brian Candler
2012-02-03 19:03           ` Christoph Hellwig
2012-02-03 21:01             ` Brian Candler
2012-02-03 21:17               ` Brian Candler
2012-02-05 22:50                 ` Dave Chinner
2012-02-05 22:43               ` Dave Chinner
2012-01-31 14:52     ` Christoph Hellwig
2012-01-31 21:52       ` Brian Candler
2012-02-01  0:50         ` Raghavendra D Prabhu
2012-02-01  3:59         ` Dave Chinner
2012-02-03 11:54       ` Brian Candler
2012-02-03 19:42         ` Stan Hoeppner
2012-02-03 22:10           ` Brian Candler
2012-02-04  9:59             ` Stan Hoeppner
2012-02-04 11:24               ` Brian Candler
2012-02-04 12:49                 ` Stan Hoeppner
2012-02-04 20:04                   ` Brian Candler
2012-02-04 20:44                     ` Joe Landman
2012-02-06 10:40                       ` Brian Candler
2012-02-07 17:30                       ` Brian Candler
2012-02-05  5:16                     ` Stan Hoeppner
2012-02-05  9:05                       ` Brian Candler [this message]
2012-01-31 20:06     ` Dave Chinner
2012-01-31 21:35       ` Brian Candler

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