Date: Fri, 08 Jun 2007 18:17:24 -0700 From: Bakul Shah <bakul@bitblocks.com> To: Josef Karthauser <joe@FreeBSD.org> Cc: current@FreeBSD.org Subject: Re: zfs drive configurations? Message-ID: <20070609011724.B97CD5B52@mail.bitblocks.com> In-Reply-To: Your message of "Fri, 08 Jun 2007 23:35:00 BST." <20070608223500.GA1250@genius.tao.org.uk>
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> I've got a machine I'm putting together with 5 drive bays, and I'm
> trying to work out what combination of drives to use. The appeal of zfs
> is that I can start with relatively small drives, and replace them, on a
> one-by-one basis, as they either die, or I get my hands on larger ones.
> Is this possible?
Yes. [In theory. I have not tried this yet]
> What if I have 5 200gb drives configured as a raidz pool, and then I
> replace one of the 200gb drives with a 400gb one. Operationally what
> would I do?
I believe you can do something like
zpool replace <pool> <device>
The new device will get "resilvered" -- get all the missing
data put on it and then brought up for operation. This can
take a while.
Note that you will not be able to use the extra disk until
*all* the disks in a group (mirror or raid) have been
replaced with bigger disks.
Also realize that while raidz gives you more space, in
general it will be slower than mirroring for random IO. If
each disk does N random ops/sec, then a 4 disk raidz will
given N random reads/sec, while a 2 stripe 2 way mirror will
give you upto 4N random reads/sec.
See
http://blogs.sun.com/roch/category/ZFS
http://www.solarisinternals.com/wiki/index.php/ZFS_Best_Practices_Guide
BTW, you can experiment using memory devices backed with real files!
With 5 disks I'd use four for one zfs pool and the last one for
temp space, and other misc. things.
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