On Fri, Nov 23, 2007 at 07:01:56PM +0100, Gert Lynge wrote: > >The disks themselves handle the checksumming to detect bad blocks. > >With modern disks it is *very* rare that a block on the disk goes bad > >without the disk being able to report it it as such. > >This means that if you have a functioning RAID1 setup and one of the > >disks report a bad block, then the controller can simply read the > >corresponding block from the other disk, and rewrite it to the disk > >with the bad block. If a disk has problems writing a block it will > >transparently re-map the block to another. > >The problems can occur when one disk in a RAID-array has failed and you > >try to rebuild it from the other disk(s). If you then encounter a bad block > >on that disk you have a problem since you don't have a good copy of that > >block. > >This is what verification (which, btw, is not the same as synchronization) > >tries to prevent by reading every block on each disk on a regular basis. > >Then the RAID controller can recover the data on any bad blocks from the > >other disk(s) in the array. > > I've been wondering how to do this with a BIOS assisted soft raid for some > time. > I have a server with ad4 ad6 in a mirror detected as ar0: > ---- > ws# atacontrol status ar0 > ar0: ATA RAID1 subdisks: ad4 ad6 status: READY > ---- > ws# cat /var/run/dmesg.boot > [...] > ar0: 76316MB <Intel MatrixRAID RAID1> status: READY > ar0: disk0 READY (master) using ad4 at ata2-master > ar0: disk1 READY (mirror) using ad6 at ata3-master > [...] > ---- > > ...and was wondering if dd could not do the job for me? > ---- > ws# man dd > [...] > EXAMPLES > Check that a disk drive contains no bad blocks: > dd if=/dev/ad0 of=/dev/null bs=1m > [...] > ---- > > What if I run: > dd if=/dev/ad4 /of=/dev/null bs=1m > dd if=/dev/ad6 /of=/dev/null bs=1m > > ...once a week - will that not verify that the two drives can read all > blocks?
Yes. If those complete without any errors then you know that the disks are fine. If one of the disks show a bad block you could then try using 'dd' to copy that block from the other disk. Hopefully this will not confuse the ataraid(4) code. It shouldn't, but you never know. > > It would be nice to limit the load (the throughput of dd) though - anyone > know if that is possible? Maybe by pipeing through a second command (I guess > a throughput limiter could easily be programmed?). > -- <Insert your favourite quote here.> Erik Trulsson [EMAIL PROTECTED] _______________________________________________ email@example.com mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"