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Re: [zfs-discuss] Can ZFS dynamically grow pool sizes? (re: Windows Home

Subject: Re: [zfs-discuss] Can ZFS dynamically grow pool sizes? re: Windows Home Server
From: Erik Trimble
Date: Wed, 12 Aug 2009 12:11:32 -0700
Take a look back through the mail archives for more discussion about this topic (expanding zpools).
The short answers are:

John Klimek wrote:
I'm a software developer with a little bit of experience in Linux but I've been 
wanting to build a fileserver and I've recently heard about ZFS.

Right now I'm considering Windows Home Server because I really don't need every 
file mirrored/backed-up but I do like what I heard about ZFS.

Anyways, if I have a bunch of different size disks (1.5 TB, 1.0 TB, 500 GB, 
etc), can I put them all into one big array and have data redundancy, etc?  
(RAID-Z?)

Yes. RAID-Z requires a minimum of 3 drives, and it can use different drives. Depending on the size differences, it will do the underlying layout in different ways. Depending on the number and size of the disks, ZFS is likely the best bet for using the most total space.

Can I also expand that array at any time?

Not in the traditional "I'm adding 1 drive to a 3-disk RAIDZ to make it a 4-disk RAIDZ". See the archives for how zpool expansion is done.
One thing that I definitely want is one single network share (\\server\movies) 
that I can transfer files to and have ZFS figure out how to place them across 
my disks.  I'd then like to able to add any size disk to my server and expand 
that storage space.

This is more a function of Samba (the sharing portion). How the data is stored on disk is a function of any volume manager (ZFS included), and will be done automatically.
Is this possible with ZFS?
Not really. Adding random size disks in random amounts isn't optimal for ANY volume manager, not just ZFS. Due to the way raid sets are set up in a volume manager, you may or may not be able to use the entire new disk space, you may or may not be able to add it to the RAID volume at all, and/or you may or may not be able to migrate the existing RAID set to a different kind of RAID set (i.e. move a RAID5 to RAID6, etc.) No current volume manager or hardware RAID card can do what you want - that's an incredibly difficult thing to ask.

ZFS works best with groups of identical disks, and can be expanded by adding groups of identical disks (not necessarily of the same size as the originals). Once again, please read the archives for more information about expanding zpools.


--
Erik Trimble
Java System Support
Mailstop:  usca22-123
Phone:  x17195
Santa Clara, CA

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