[mythtv-users] Why RAID 5 stops working in 2009

Travis Tabbal travis at tabbal.net
Fri Oct 24 14:54:11 UTC 2008

On Fri, Oct 24, 2008 at 3:27 AM, Ma Begaj <derliebegott at gmail.com> wrote:

> Last time I read about ZFS I was not able to find any special features
> which could not be done with RAID and LVM. Snapshots are pretty nice
> feature, but FreeBSD had it years ago and I never used it much because
> it was no solution for backup. And snapshots made with ZFS can also be
> made with "cp" and hard linking.

There is one feature ZFS has that makes it my choice for large filesystems
(>1TB). Checksums. It can detect that the data on the disk is bad, and WHICH
copy is bad. RAID5 can't do that. It can tell something's wrong, but not how
to fix it. XOR can't tell you that, not when the drives don't report the
error. That means my next NAS machine will be running OpenSolaris or
FreeBSD. I'd prefer to run Linux on all my servers just because I'm more
familiar with it and it seems to have better hardware support, but I'm not
willing to use ext3 on larger filesystems. fsck takes too damn long and with
a system that big, silent corruption is a very real concern. ZFS also seems
to me to be more flexable in the long run than LVM/mdadm.

For backups, I'm already using rsnapshot, so the filesystem based snapshots
aren't that big of a deal to me. However, they do apear to be significantly
faster to create than rsnapshot is. So I might try them when I do get a ZFS
based system running. Linux will still live on a large part of my network
though, the hardware and software support is simply much better there. Of
course, snapshots are only one small part of a backup soultion.
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