zfs discuss - Mar 2010 - Convert from rz2 to rz1

Is it possible to convert a rz2 array to rz1 array?

I have a pool with to rz2 arrays. I would like to convert them to rz1. Would
that be possible?

If not, is it ok to remove one disk from a rz2 array and just let the array keep
running with one disk missing?

Regards,

Lars-Gunnar Persson
System Administrator

Nansen Environmental and Remote Sensing Center
Address: Thorm?hlensgate 47, 5006 Bergen
Direct: +47 55 20 58 31, switchboard: +47 55 20 58 00, fax: +47 55 20 58 01
Internet: http://www.nersc.no, e-mail: lars-gunnar.persson at nersc.no

On Thu, 11 Mar 2010, Lars-Gunnar Persson wrote:
> Is it possible to convert a rz2 array to rz1 array? I have a pool with
> to rz2 arrays. I would like to convert them to rz1. Would that be
> possible?
No, you''ll have to create a second pool with raidz1 and do a "send
| recv" operation to copy the data over.
> If not, is it ok to remove one disk from a rz2 array and just let the
> array keep running with one disk missing?
The pool will be degraded if you do that, but continue to work as it has enough
redundancy to retrieve the data. However, zfs will use the remaining disks to
continue to write double parity, so your overall capacity will go down
proportionally.  For example, if you have five disks in a raidz2 group, whenever
you write a block of data to disk A, then two other disks, B and C for example,
will get parity information.  If you pull disk B out, then you lose the
double-parity protection, but you''ll still have access to your data,
and the ability to repair it if you lose the block written to A.

Pulling disk B will not stop future writes from getting two parity blocks. For
example: the next write to A will get parity blocks written to, e.g., C and D.
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