Check the thread started by Matthias within last week.

On Sun, Sep 20, 2009 at 12:36 PM, John Robinson
[off-list ref] wrote:

On 19/09/2009 17:10, Greg Freemyer wrote:
[...]

quoted

I don't know how specifically, but it also seems to me the mdraid
stack could add to currently poor data integrity process even in the
absence of a supporting scsi subsystem.  Maybe by pulling out the
integrity checksum / crc info and putting it on yet another disk, or
mixing it in with the parity calculation.

Specifically you could steal the second parity stripe from a raid 6
setup and replace it with this end-to-end data integrity checksum /
crc.  The checksum / crc is much smaller than the original data so the
one integrity disk should support a reasonable number of data disks.
Obviously this would not be one of the formal raid levels, but that
doesn't mean its not useful.

I vaguely remember someone here was prototyping/developing a device mapper
thingy which added checksumming/integrity to simulate high-end RAID cards
adding a checksum to each 512-byte sector by using 520- or 528-byte sectors
on their component discs. I don't remember the details, but what I have in
mind was something along the lines of using an extra sector on the
underlying device per 64 sectors or so. There wouldn't be too heavy an
overhead on small reads - we do readahead anyway - and it would make small
writes even more painful than they are already, but shouldn't significantly
reduce throughput on large (chunk size) reads and writes. I'd use it.

Cheers,

John.
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