[zfs-code] Expanding a raidz pool?

Ty Newton
Sat, 29 Aug 2009 03:22:32 -0000

Hi,
I''ve read a few articles about the lack of ''simple''
raidz pool expansion capability in ZFS.  I am interested in having a go at
developing this functionality.  Is anyone working on this at the moment?

I''ll explain what I am proposing.  As mentioned in many forums, the
concept is really simple: allow a raidz pool to grow by adding one or more disks
to an existing pool.  My intended user group is the consumer market, as opposed
to the enterprise, so I expect I''ll put some rather strict limitations
on how/when this functionality will operate: to make the first implementation
more achievable.

The use case I will try and solve first is, what I see as, the simplest.  I have
a raidz pool configured with 1 file system on top; no snapshots.  I want to add
an additional disk (must be at least the same size as the rest of the disks in
the pool).  I don''t mind if there is some downtime.  I want all my data
to take advantage of the additional disk.

What is the benefit to the consumer?  The answer is simple:
- more flexibility in growing storage i.e. can have an odd number of disks.
- more disk space available for use e.g. 2 pools of 3 disks gives less available
space than 1 pool of 6 disks.
- consistent with many RAID-5 implementations
- opens up the consumer market for raidz: growable small backup/SAN/Home Theatre
appliances


I''m no expert on any of this stuff, but I do have many years experience
as a software engineer.  Is there a mentoring program that Sun offers so I can
get some assistance when necessary?  My expectation is that this isn''t
impossible to do but it isn''t simple to do either.

Are there any procedural hoops I need to jump through to take on this piece of
work?


Regards,
Ty