Re: intent-logging, not synchronizing written blocks?

On Wednesday November 9, carlos@fisica.ufpr.br wrote:

Neil Brown (neilb@suse.de) wrote on 10 November 2005 09:50:
 >> Is intent-logging for raid5 already in mainline or only in -mm? I
 >> looked for it in 2.6.14 and found nothing...
 >
 >raid5 is in 2.6.14.  raid6 and raid10 should be in 2.6.16.
 >What did you look for?

Some doc, or compilation option. I suppose it's always on then and
just using --re-add with mdadm is enough.

No, you have to tell an md array to use an intent bitmap.
If you can do this to a running array with e.g.
  mdadm --grow --bitmap=internal /dev/md1

 >I'm not sure what you mean by 'went out of sync'.

I wasn't clear, I meant a device failed.

 >When an array is active and being written to, many stripes could be
 >out-of-sync at any time, as writes have been started, but haven't
 >completed yet. Intent logging record the intent to write somewhere
 >before doing the write, and then clears the intent sometime after
 >the write completes.
 >
 >After a crash, some intents will still be recorded, and only the
 >stripes associated with these risk being out-of-sync, so only those
 >need to be resynced.

What about the writes that were started and completed after the
failure?

If the array is degraded, intents are not removed from the bitmap, so
these writes will still be recorded in the bitmap.

NeilBrown