On Wed, 21 Mar 2012, maillist reader wrote:

I read though that ZFS does not have a "defragmentation" tool, is this still 
the case? It would seem with such a
performance difference between "sequential reads" and "random reads" for 
raidzN's, a defragmentation tool would be
very high on ZFS's TODO list ;).

Zfs does not usually suffer significantly from fragmentation. To be clear, "random reads" means random file access and necessary head seeks. Any mechanical-based device will suffer from this and it is not specific to zfs.

Something which is specific to zfs is that within a zdev, a stripe must be read and written completely. Partial stripe reads are not supported since a full read is necessary in order to validate the block checksum.

Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
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