Re: mismatch_cnt again

Piergiorgio Sartor
2009-11-08T16:04:33Z

Hi,

> But unless your drive firmware is broken the drive with only ever give
> the correct data or an error. Smart has a counter for blocks that have
> gone bad and will be fixed pending a write to them:
> Current_Pending_Sector.
>
> The only way the drive should be able to give you bad data is if
> multiple bits toggle in such a way that the ECC still fits.

Not really, I've disks which are *perfect* in smart sense
and nevertheless I had mistmatch count.
This was a SW problem, I think now fixed, in RAID-10 code.

This means that, yes, there could be mismatches, without
any warning, from other sources than disks.
And these could be anywhere in the system.
I already mentioned, time ago, a cabling problem which was
leading to a similar result: wrong data on different disks,
without any warning or error from the HW layer.

That is why it is important to know *where* the mismatch
occurs and, if possible, in which device component.
If it is an empty part of the FS, no problem, if it
belongs to a specific file, then it would be possible
to restore/recreate it.

Of course, a tool will be needed telling which file is
using a certain block of the device.

bye,

--

piergiorgio