[zfs-discuss] ashift=12 on 512 bytes disks?
g.danti at assyoma.it
Sun Dec 17 04:05:06 EST 2017
I recently created a new ZFS pool using 4x WD Gold 2TB (configured in
mirrored pairs) and 2x Samsung 850 EVO 500GB for caching ans SLOG.
The main pool disks (WD Gold) have 512-bytes sectors and I left ashift
to the default value (ashift=9). Cache and SLOG were added with "-o
ashift=12" to align at 4K boundaries.
Now I wonder if the original choice to use ashift=9 on the main disks
was the better one, or if it can bite me in the future. Suppose a disk
fails and I can not replace it with another 512-bytes disk, rather a 4K
HD must be used. I know I can manually set the correct ashift value (12)
during replacing; however, I wonder if this "mixed" mode (ashift=9 on
some disks, ashift=12 on the new 4K one) can lead to lower performance
and/or other problems.
The obvious solution would be to recreate the entire pool with
ashift=12, treating all disks as 4K ones. I know this implies some space
loss, but it should be no too severe.
Assyoma S.r.l. - www.assyoma.it
email: g.danti at assyoma.it - info at assyoma.it
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