[PVE-User] SAN recommendation.

Michael Rasmussen mir at miras.org
Wed Aug 28 10:59:04 CEST 2013


On 08-28-2013 09:50, Muhammad Yousuf Khan wrote: 

> one more question. as i am trying to study ZFS from googling and youtubing. i have a question like we mdadm in linux can we create RAID partitions for ZFS? for example.if i am using RAIDz1 with 3x500GB HD . means it is giving me (1TB). so for example after few years may be 2 years on out of 3 drives fail and 500 drive is no longer available in market and at that time minimum size i can by is 1TB. so my question can i plug large size drive as RAID with small drives one?

The building block of a ZFS pool is vdevs (virtual device). A vdev can
be a mirror, raidz1, raidz2, raidz3. If a zpool contains more than one
vdev writes are stripped across all vdevs. A raid can be made of any
number of disks. Restrictions to size, RPM etc. are restricted to vdevs
only so in any vdev all disks should share size, speed, and block size.

An excellent guide can be found here:
http://nex7.blogspot.dk/2013/03/readme1st.html [1]

Your specific question regarding disk replacement. You can always
upgrade the individual disks in a vdev but until all disks have equal
size the available space of any disk will be determined by the lowest
common denominator. In your case this will mean adding a 1TB disk to the
vdev will only make 500MB usual of that disk until every disk the vdev
is replaced with 1TB disk. So when the last disk in the vdev is replaced
by a 1TB disk the total available size of the vdev will increase from
1TB to 2TB. You should also remember that it is better to have 2 1TB
disks than 1 2TB disk since writes will be stripped when the number of
disks is greater than 1. In general the recommendation is not to use
disks larger than 1TB.

Michael Rasmussen

[1] http://nex7.blogspot.dk/2013/03/readme1st.html
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