Richard Elling wrote:
Robert Milkowski wrote:
Hello Richard,

Wednesday, March 21, 2007, 1:48:23 AM, you wrote:

RE> Yes, PSARC 2007/121 integrated into build 61 (and there was much rejoicing :-)
RE> I'm working on some models which will show the affect on various RAID
RE> configurations and intend to post some results soon. Suffice to say, if RE> you have a stripe with > 1 disk, you might be able to survive loss of a RE> disk. There are some other details which will need to be fleshed out, too. RE> More importantly, positioning this relative to the other options can be RE> confusing, and we're working on clear explainations to help avoid over-
RE> exuberance.

Also I guess it would be possible to change copies once file system is
created, right? If it's so then people could get confused about which
data are protected and to what extent and which are not.

My understanding is that writes use the current copies parameter.  So, yes,
some people could be confused.  A good idea would be to set that policy at
file system creation time.

That's right.  Here are the manpage changes:

     copies=1 | 2 | 3

         Controls the number of copies of data stored for this dataset.
         These copies are in addition to any redundancy provided by the
         pool (eg. mirroring or raid-z).  The copies will be stored on
         different disks if possible.

         Changing this property only affects newly-written data.
         Therefore, it is recommended that this property be set at
         filesystem creation time, using the '-o copies=' option.

Perhaps 'zfs rewrite' would possibly help (someone working on this?).

Wouldn't that fall under the generic rewrite/shrink functionality we're also anxiously waiting for?


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