On Wed, Apr 14, 2010 at 08:48:42AM -0500, Paul Archer wrote: > So I turned deduplication on on my staging FS (the one that gets mounted > on the database servers) yesterday, and since then I've been seeing the > mount hang for short periods of time off and on. (It lights nagios up > like a Christmas tree 'cause the disk checks hang and timeout.)
Does it have enough (really, lots) of memory? Do you have an l2arc cache device attached (as well)? Dedup has a significant memory requirement, or it has to go to disk for lots of DDT entries. While its doing that, NFS requests can time out. Lengthening the timeouts on the client (for the fs mounted as a backup destination) might help you around the edges of the problem. As a related issue, are your staging (export) and backup fileystems in the same pool? If they are, moving from staging to final will involve another round of updating lots of DDT entries. What might be worthwhile trying: - turning dedup *off* on the staging filesystem, so NFS isn't waiting for it, and then deduping later as you move to the backup area at leisure (effectively, asynchronously to the nfs writes). - or, perhaps eliminating this double work by writing directly to the main backup fs. -- Dan.
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