Re: Request for opinions - gvinum or ccd?

On Mon, 1 Jun 2009 00:59:43 +0100
xorquewasp@googlemail.com wrote:

> There is one last thing I'd like clarified. From the zpool
> manpage:
> 
>   In order  to take advantage of these features, a pool must make use of
>   some form of redundancy, using either mirrored or raidz  groups.  While
>   ZFS  supports running in a non-redundant configuration, where each root
>   vdev is simply a disk or file, this is strongly discouraged.  A  single
>   case of bit corruption can render some or all of your data unavailable.
> 
> Is this supposed to mean:
> 
>   "ZFS is more fragile than most. If you don't use redundancy, one
>    case of bit corruption will destroy the filesystem"
> 
> Or:
> 
>   "Hard disks explode often. Use redundancy."

How about (from an old disk recover paper):

    Disks, unlike software, sometimes fail. Using redundancy can help
    you prevent this from resulting in data loss.

That said, there aren't many file systems that can recover from data
errors in the underlying storage. ZFS appropriately configured is one.
I don't believe the default config is appropriate, though. You need
both checksum on and copies > 1 on, and the latter isn't the
default. It's probably better to let zpool provide the redundancy via
a mirror or raid configuration than to let zfs do it anyway.

       <mike
-- 
Mike Meyer <mwm@mired.org>		http://www.mired.org/consulting.html
Independent Network/Unix/Perforce consultant, email for more information.

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