Backup strategy for large mailbox stores

Vincent Fox vbfox at
Mon Feb 15 22:08:43 EST 2010

John Madden wrote:
> Out of curiousity, how good is zfs with full fs scans when running in  
> the 100-million file count range?  What do you see in terms of  
> aggregate MB/s throughput?

I'm not sure what you mean by "full fs scan" precisely, and
haven't tested anything very large.  Since the design allows
up to 2^48 files PER DIRECTORY and 2^78 bytes per pool
I hope they have thought through very large performance.
But I don't recall seeing any benchmarks deliberately on
very large numbers of small files.  The design uses hundreds
of metaslabs per device, not bitmaps or b-trees, so it's quite
different than what old admins like me were used to.  The first
thing you notice is "how many inodes do I need" at filesystem
creation time is no longer something you need worry about.
If the pool has space you can create more files.

Our performance is very good with backends up to 10K users
and zpool scrub is about the only thing I can run that pushes
iostat numbers up to 99.  I don't notice an performance
degradation when scrub is running.  FWIW our pools and
systems are fairly idle but maybe this helps:

# zpool iostat
               capacity     operations    bandwidth
pool         used  avail   read  write   read  write
----------  -----  -----  -----  -----  -----  -----
ms11         323G   757G     51     52   626K   400K

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