On Aug 21, 2010, at 3:36 PM, Toby Thain wrote:
> On 21-Aug-10, at 3:06 PM, Ross Walker wrote:
>> On Aug 21, 2010, at 2:14 PM, Bill Sommerfeld <bill.sommerf...@oracle.com>
>> wrote:
>>> On 08/21/10 10:14, Ross Walker wrote:
>>> ...
>>>> Would I be better off forgoing resiliency for simplicity, putting all my
>>>> faith into the Equallogic to handle data resiliency?
>>>
>>> IMHO, no; the resulting system will be significantly more brittle.
>>
>> Exactly how brittle I guess depends on the Equallogic system.
>
> If you don't let zfs manage redundancy, Bill is correct: it's a more fragile
> system that *cannot* self heal data errors in the (deep) stack. Quantifying
> the increased risk, is a question that Richard Elling could probably answer :)
The risk of data loss isn't very different between ZFS and a hardware RAID
array.
The difference is the impact of the loss. What we've observed over the years is
that older generation or "budget" RAID arrays that do not verify the data and
will
happily pass corrupted data up the stack. ZFS will detect this, providing two
important control points:
1. The "silent" error is silent no more -- the corrupted file will be noted in
the logs
and the output of "zpool status -xv" This is a huge win for the recovery effort
because you can quickly determine the scope of the damage and plan a recovery
from backups, if needed.
2. The policy on how to present this information to the application requesting
data
and the systems administrator is somewhat flexible. See the "failmode" property
in
the zpool(1m) man page.
If I may put it in order of preference:
+ Minimum effort: protect your data using regular backups
+ Better: add RAID of some sort to protect against whole disk failure
+ Best: add ZFS for data management, end-to-end error detection,
copies, etc.
-- richard
--
OpenStorage Summit, October 25-27, San Fransisco
http://nexenta-summit2010.eventbrite.com
Richard Elling
rich...@nexenta.com +1-760-896-4422
Enterprise class storage for everyone
www.nexenta.com
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