ZFS with errors

[Paul Mather]

Luciano,

> Date: Wed, 13 Apr 2016 16:22:51 +0200
> From: Luciano Mannucci <luciano at vespaperitivo.it>
> To: freebsd-questions at freebsd.org
> Subject: Re: ZFS with errors
> Message-ID: <3qlQxr34YhzRRqQ at baobab.bilink.it>
> Content-Type: text/plain; charset=iso-8859-1
> 
> On Wed, 13 Apr 2016 15:56:20 +0200 (CEST)
> Trond Endrest?l <Trond.Endrestol at fagskolen.gjovik.no> wrote:
> 
>> There's no redundancy in this pool, making it hard for ZFS to 
>> automatically repair your files.
>> 
>> Maybe you should destroy your pool and recreate it using a mirrored 
>> configuration. Maybe, mirror disks 1 & 2, and disks 3 & 4, e.g.
> They are of different sizes. I don't know if I can add redundancy
> without loosing the bits that exeed the smallest one...
> I'm a zfs newbie, just experimenting by now... :)
> 
> Thanks anyway,
> 
> Luciano.


The only way you can add redundancy to the type of pool you have (i.e., several drives concatenated together without any mirroring or raidz redundancy) is to set the "copies=..." property on datasets for which you want some redundancy:

     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, for
         example, mirroring or RAID-Z. The copies are stored on different
         disks, if possible. The space used by multiple copies is charged to
         the associated file and dataset, changing the used property and
         counting against quotas and reservations.

         Changing this property only affects newly-written data. Therefore,
         set this property at file system creation time by using the -o
         copies=N option.



Note the "Changing this property only affects newly-written data" part, though. You could also apply this selectively if you don't want to lose too much pool space, e.g., to impart some redundancy to files in your home directory but not to other areas where data loss can easily be remedied or isn't as much of a problem (/usr/src; /usr/ports; /usr/obj; etc.).

Cheers,

Paul.