> Use a faster processor or change to a mirrored configuration. > raidz2 can become processor bound in the Reed-Soloman calculations > for the 2nd parity set. You should be able to see this in mpstat, and to > a coarser grain in vmstat.
Hmm. Is the OP's hardware *that* slow? (I don't know enough about the Sun hardware models) I have a 5-disk raidz2 (cheap SATA) here on my workstation, which is an X2 3800+ (i.e., one of the earlier AMD dual-core offerings). Here's me dd:ing to a file on FreeBSD on ZFS running on that hardware: promraid 741G 387G 0 380 0 47.2M promraid 741G 387G 0 336 0 41.8M promraid 741G 387G 0 424 510 51.0M promraid 741G 387G 0 441 0 54.5M promraid 741G 387G 0 514 0 19.2M promraid 741G 387G 34 192 4.12M 24.1M promraid 741G 387G 0 341 0 42.7M promraid 741G 387G 0 361 0 45.2M promraid 741G 387G 0 350 0 43.9M promraid 741G 387G 0 370 0 46.3M promraid 741G 387G 1 423 134K 51.7M promraid 742G 386G 22 329 2.39M 10.3M promraid 742G 386G 28 214 3.49M 26.8M promraid 742G 386G 0 347 0 43.5M promraid 742G 386G 0 349 0 43.7M promraid 742G 386G 0 354 0 44.3M promraid 742G 386G 0 365 0 45.7M promraid 742G 386G 2 460 7.49K 55.5M At this point the bottleneck looks architectural rather than CPU. None of the cores are saturated, and the CPU usage of the ZFS kernel threads is pretty low. I say architectural because writes to the underlying devices are not sustained; it drops to almost zero for certain periods (this is more visible in iostat -x than it is in the zpool statistics). What I think is happening is that ZFS is too late to evict data in the cache, thus blocking the writing process. Once a transaction group with a bunch of data gets committed the application unblocks, but presumably ZFS waits for a little while before resuming writes. Note that this is also being run on plain hardware; it's not even PCI Express. During throughput peaks, but not constantly, the bottleneck is probably the PCI bus. -- / Peter Schuller PGP userID: 0xE9758B7D or 'Peter Schuller <[EMAIL PROTECTED]>' Key retrieval: Send an E-Mail to [EMAIL PROTECTED] E-Mail: [EMAIL PROTECTED] Web: http://www.scode.org
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