Erik Trimble wrote:
If you had known about the drive sizes beforehand, the you could have
done something like this:
Partition the drives as follows:
A: 1 20GB partition
B: 1 20gb & 1 10GB partition
C: 1 40GB partition
D: 1 40GB partition & 2 10GB paritions
then you do:
zpool create tank mirror Ap0 Bp0 mirror Cp0 Dp0 mirror Bp1 Dp1
and you get a total of 70GB of space. However, the performance on this
is going to be bad (as you frequently need to write to both partitions
on B & D, causing head seek), though you can still lose up to 2 drives
before experiencing data loss.
It is not clear to me that we can say performance will be bad
for stripes on single disks. The reason is that ZFS dynamic
striping does not use a fixed interleave. In other words, if
I write a block of N bytes to a M-way dynamic stripe, it is
not guaranteed that each device will get an I/O of N/M size.
I've only done a few measurements of this, and I've not completed
my analysis, but my data does not show the sort of thrashing one
might expect from a fixed stripe with small interleave.
-- richard
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