Date: Wed, 06 Aug 2014 01:23:35 -0500 From: Scott Bennett <bennett@sdf.org> To: Daniel Staal <DStaal@usa.net> Cc: freebsd-questions@freebsd.org Subject: Re: gvinum raid5 vs. ZFS raidz Message-ID: <201408060623.s766NZ64028954@sdf.org>
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On Sat, 02 Aug 2014 18:33:38 -0400 Daniel Staal <DStaal@usa.net> wrote:
>--As of August 2, 2014 1:21:54 AM -0500, Scott Bennett is alleged to have
>said:
>
>>>> Does not support migration to any other Does not support migration
>>>> RAID levels or their equivalents. between raidz levels, even by
>>>
>>> Correct. Once you have created a vdev, that vdev must remain the same
>>> type. You can add mirrors to a mirror vdev, but you cannot add drives or
>>> change raid level to raidz1, raidz2, or raidz3 vdevs.
>>
>> Too bad. Increasing the raidz level ought to be not much more
>> difficult than growing the raidz device by adding more spindles. Doing
>> the latter ought to be no more difficult that doing it with gvinum's
>> stripe or raid5 devices. Perhaps the ZFS developers will eventually
>> implement these capabilities. (A side thought: gstripe and graid3
>> devices ought also to be expandable in this manner, although the resulting
>> number of graid3 components would still need to be 2^n + 1.)
>
>--As for the rest, it is mine.
>
>There actually is a semi-simple way, even if it's not direct...
>
>You can 'send' a ZFS filesystem to a backup drive, and then 'receive' it
>back to a new pool. It will keep all file and volume level options when
>you do that, but the pools can be set up differently. It's not something
>you can do in-place, but it's not hard either.
Right, and that's why it is actually *not* a way. A "grow" operation,
as implemented in gvinum(8), is done in place.
>
>(Basically, it's a simplified 'backup and restore to new setup', but it is
>majorly simplified.)
>
That would mean having/buying enough more space to be able to do that.
Further, one would probably want to set up a new raidzN on those devices
to hold all that output, so that one would not risk corrupting/losing one's
data during the process. And if one is going to do that, then why copy it
back? Growing it in place would eliminate that space requirement, perhaps
saving the owner a considerable amount of money. The only additional
spindles needed would be the new ones to increase the space or raidz level.
Scott Bennett, Comm. ASMELG, CFIAG
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