Recently, however, it has started taking over 20hours to complete. Not much has
happened to it in that time: A few extra files added, maybe a couple of
deletions, but not a huge amount. I am finding it difficult to understand why
performance would have dropped so dramatically.
FYI the server is my dev box running Solaris 11 express, 2 mirrored pairs of
1.5GB SATA disks for data (at v28), a separate root pool and a 64GB SSD for
L2ARC. The data pool has 1.2TB allocated.
Can anyone shed some light on this?
all I can tell you is that I've had terrible scrub rates when I used dedup. The
DDT was a bit too big to fit in my memory (I assume according to some very
basic debugging). Only two of my datasets were deduped. On scrubs and resilvers
I noticed that sometimes I had terrible rates with < 10MB/sec. Then later it
rose up to < 70MB/sec. After upgrading some discs (same speeds observed) I got
rid of the deduped datasets (zfs send/receive them) and guess what: All of the
sudden scrub goes to 350MB/sec steady and only take a fraction of the time.
While I certainly cannot deliver all the necessary explanations I can only tell
you that from my personal observation simply getting rid of dedup speeded up my
scrub times by factor 7 or so (same server, same discs, same data).
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