ZFS guidelines - preparing for future storage expansion

[Andrew Snow]

Zaphod Beeblebrox wrote:
> I moved from 5x 750G to 5x 1.5T disks this way earlier this year.  It takes
> a _long_ time.  resilvering 750g (they were about 98% full when I did this)
> onto the 1.5T disks took about 12 hours each.

Currently there is no "read-ahead" for scrubbing and resilvering, so it 
only talks to one disk and at a time and proceeds using only about half 
the I/O capacity of your disks (or less). Read-ahead is one of the 
planned features for ZFS next year.

Also, when your disks are 98% or more full and you are doing any writes 
at all ZFS spends a long time looking for free blocks with an 
inefficient algorithm.  An improved "disk full" algorithm is also 
planned for next year.


- Andrew