Sounds like it could be wrapping around as suggested. Since you are
swapping out all the disks have you thought about stopping the array
and using dd to copy the old disk to the new disk. Then there is no
resync period or degraded array.

Ryan

On Thu, May 14, 2009 at 9:58 AM, Bryan Mesich [off-list ref] wrote:

On Thu, May 14, 2009 at 03:06:47PM +0200, Rainer Fuegenstein wrote:

quoted

Hi guys,

I'm a but confused about the duration of a raid5 resync:

- occasionally, my server with 4*750 gb sata raid5 crashed (because of
problems with the power supply); after rebooting it took about 10 to 12
hours to resync the raid5 (guess it just re-created some parity
information or however it works internally, but didn't have to copy
any data)

- right now I replaced one 750GB disk with a 1.5TB disk, but now
resyncing (according to /proc/mdstat) it is supposed to take only 160
minutes ?! although it needs top copy data to a blank disk ?

Just a guess...but your problem might be an artifact of a bug
that has been recently fixed.  Neil sent out mail on 2009-05-04
with the fix I'm thinking about.  Here is an excerpt from his
mail:

Subject: [md PATCH 4/7] md: tidy up status_resync to handle
large arrays.

Two problems in status_resync.
1. It still used Kilobytes as the basic block unit, while most
  code now uses sectors uniformly.
2. It doesn't allow for the possibility that max_sectors exceeds
  the range of "unsigned long".

So
 - change "max_blocks" to "max_sectors", and store sector numbers
  in there and in 'resync'
 - Make 'rt' a 'sector_t' so it can temporarily hold the number
  of remaining sectors.
 - use sector_div rather than normal division.
 - change the magic '100' used to preserve precision to '32'.
  + making it a power of 2 makes division easier
  + it doesn't need to be as large as it was chosen when we
  averaged speed over the entire run.  Now we average speed over the
  last 30 seconds or so.

quoted

is this normal or should I be worried, especially before I pull out
the next 750GB disk and replace it with the next 1.5TB disk ?

If your sync only takes 160 minutes...then I'd start to poke
around.  If its finishing time is reasonable considering the
array size, then I'd continue with the migration.

quoted

tnx in advance.

Bryan

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