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[Bug 590650] md: raid1 with 1/2 disks and bitmap is VERY SLOW
  • From: bugzilla_noreply@xxxxxxxxxx
  • Date: Fri, 2 Apr 2010 21:03:22 +0000
  • Message-id: <20100402210322.835BD245467@xxxxxxxxxxxxxxxxxxxxxx>
http://bugzilla.novell.com/show_bug.cgi?id=590650

http://bugzilla.novell.com/show_bug.cgi?id=590650#c1


Neil Brown <nfbrown@xxxxxxxxxx> changed:

What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |INVALID

--- Comment #1 from Neil Brown <nfbrown@xxxxxxxxxx> 2010-04-02 21:03:21 UTC ---
Yes, there it a speed penalty for using a bitmap. It is quite
dependant on write load. You are probably doing lots of
sequential writes to get that difference you report.
Increasing the bitmap chunksize could help.

Even in a degraded raid1 it is important to update the bitmap on
all writes to new chunks, though we never clear bits. That way
if the missing device is added back into the array, we can recovery
it by just coping the chunks for which a bit is set in the bitmap.

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