[OpenIndiana-discuss] System disk corruption

[Jan Owoc]

On Mon, Feb 20, 2012 at 7:38 AM, Robin Axelsson
<gu99roax at student.chalmers.se> wrote:
> It is evident that ZFS is not very good to use without disk redundancy.

In your case, you would have silent data corruption on-disk. This
corrupted data would get passed to programs, that would try to work
with what they have. In some cases, you might be lucky - in others,
your system would randomly crash.

If you are frustrated about being informed about disk errors, and
would prefer the system to not check, it is possible to set
"checksum=off". This is not recommended.


On Mon, Feb 20, 2012 at 8:05 AM, Gregory Youngblood
<gregory at youngblood.me> wrote:
>> It would be great if there were some kind of software that could be set up to generate .par2 files (with x% data redundancy) on-the-fly to protect files on hard drives without disk redundancy (RAID=0).
>
> What about telling zfs to maintain more than one copy? Not sure how well data is spread out if there is only one drive though. Anyone know?

Yes, there is an option copies=2 (or 3) to have each data block have a
"ditto block" somewhere else on the filesystem. You need twice (or
three times) the capacity to do this. Both copies are still physically
on the same drive, so while this protects against random data
corruption or a few bad sectors, it does not protect against the
single drive failing.

Gregory is talking about generating something like "ECC" for each
block. Such an algorithm, for example, could be set to use an
additional 10% of information stored with the checksum to attempt
recovery of the target block. I'm not aware of any such option at the
present, but adding it would require a new zpool version.


Jan