Re: Boot from ZFS

Brooks Davis wrote:
> On Sat, Jul 12, 2008 at 10:43:09AM +1000, Duncan Young wrote:
>> Be carefull,  I've just had a 6 disk raidz array die.  Complete failure which 
>> required restore from backup (the controler card which had access to 4 of the 
>> disks, lost one disk, then a second (at which point the machine paniced, Upon 
>> reboot the raidz array was useless (Metadata corrupted)).  I'm also getting 
>> reasonably frequent machine lockups (panics) in the zfs code.  I'm going to 
>> start collecting crash dumps see if anyone can help in the next week or two.
> 
> If you look at the research on disk corruption and failure modes both
> in recent proceeding of FAST and the latest issue of ;LOGIN: it's clear
> that any RAID-like scheme that does not tolerate double faults is likely
> to fail.  In theory, zfs should tolerate certain classes of faults
> better than some other technologies, but can't deal with full disk
> double faults unless you use raidz2.

Going back to my initial question (ie: subject), I've implemented the 
box in such a way that I boot via USB disk that contains only the /boot 
partition.

This allows me to use all four entire disks in my ZFS pool instead of 
creating a UFS slice on one of them first. It then mounts / via ZFS and 
the system takes over from there.

This box IS a backup box...in the sense of convenience. We still have 
off-site backup, this is just for quick retrieval of information if the 
need arises. If this box fails, We build a new one.

That said, I did use raidz and sacrificed the equivalent of one drive. I 
did some testing (pop out a drive, reboot, etc) and it works very well. 
I do like the raidz2 idea, and when my needs justify adding more disks, 
I'll double the space and use the double protection.

> Regardless of the technology, backups are essential.  If you actually value
> your data, off-site backups are essential.

I fully agree with this statement. I've also been a long time believer 
that a backup is only as good as the time and difficulty level it takes 
to restore from it.

Steve