[Discuss] SSD drives vs. Mechanical drives

[bogstad at pobox.com (Bill Bogstad)]

On Wed, May 7, 2014 at 12:40 PM, Richard Pieri <richard.pieri at gmail.com> wrote:
> Dan Ritter wrote:
>> 3Ware tw_cli man page:
>>
>>  Verify activity attempts to verify all units based on their unit
>>  type. Verifying RAID-1 involves checking that both drives contain the
>
> It doesn't work reliably. If the data is corrupted somewhere in the
> controller itself (flakey cache for example) then the checksums will be
> correct but the data that is written and checked is wrong. I've had a
> 3Ware controller do this to me. All of the checksums matched up but the
> data was damaged prior to the calculations and writes. Correctly written
> and replicated wrong data is still wrong data. :P

And checksums can be incorrectly generated/verified by any hardware at any time.
I claim that 100% data integrity is impossible.   I don't think even
ZFS can guarantee
100% data integrity with the right set of bizarre hardware failures in
the CPU/RAM of the
computer.  Pointing out that all hardware can have errors is kind of a
moot point.
More important is being able to assess what kinds of hardware/software
failures can result in loss of integrity (or data) and their relative
probabilities.

Bill Bogstad