[zfs-discuss] n00b Question on drive partitioning for zfs

UbuntuNewbie chessdoter at googlemail.com
Wed Apr 4 01:24:55 EDT 2012

Hello list,

 i want to create a raidz pool consisting of 3 drives of different
sizes (1x1TB + 2x2TB). I understand, the smallest disk size will limit
the pools available space. Thus i will have to create partitions/
slices possibly matching the 1TB drive on the larger disks. Of course,
i can do that using MBR partitioning on the 1TB disk (whole disk). But
since the larger disks will use gpt anyway and the smaller disk will
be devoted to ZFS entirely, i would like to match the required
partition size as exactly as possible.

 If i give the smaller disk (/dev/sde) to ZFS, it creates a gpt label
and an area/partition/slice at the end, but it does NOT address the
free space like /dev/sde1, instead it references the whole disk. Now,
i am confused: How large do the partitions on the larger disks have to
be to (almost) exactly match the size, ZFS takes from /dev/sde ?

 What might complicate matters slightly: the smaller disk is an old-
format drive (1s = 512b), whereas the other 2 are newer format ones
(1s = 4k), pointing towards ashift=12. So i am searching for proper
alignment for the gpt-partitions on the newer drives.

 so: How can i find the correct (minimal) partition size to create my
raidz configuration from? Is anyone into the size calculation to hint
me towards a less space-wasting approach than mine (just matching the
number of sectors from sde whole-disk to each remaining partition on
the other 2 drives divided by 8, should be the upper bound but most
likely a waste...)

 Just in case... Its not just the gain in space that drives my
question, but the likely gain in understanding... :-)

... one happy camper since ZoL lives in my machine :-)


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