ZFS - whole disk or partition or BSD slice?

[Paul Kraus]

On Jan 27, 2013, at 8:36 PM, Shane Ambler wrote:

> I recall reading that using partitions for zfs on FreeBSD was as good as full disks. For a boot zpool we need to at least have a partition for the boot-code and one for zfs preventing the use of a full disk.

	I have been using ZFS with GPT partitions with no issues. I have NOT compared performance between whole disk and partitioned, which is where the difference in Solaris arises (ZFS makes better use of the physical drive's write cache).

> ZFS is meant to be compatible between different endian systems (x86 and sparc) From what I have read and heard it sounds like zpools are expected be compatible between different OS's as well - as far as zpool versions are compatible - but I do expect it would depend on the partition tables being readable - while full disk usage should work I would also think GPT is compatible. OSX 10.5 (x86 and ppc) included a read-only zfs kext (before Apple canned the project) so it must have been able to read Solaris or FreeBSD created zpools which does indicate a fairly high level of compatibility.

	The target OS must be able to read the partitioning scheme used. I am not aware of Solaris / OpenSolaris / Illumos being able to read GPT partitions, but it has been over 6 months since I played with any of them.

> I believe the way ZFS marks disks/partitions with the zpool data is so that the zpools can be recognised between systems and controllers - it would be interesting to know if and under what conditions a zpool can be accessed, both between different FreeBSD machines as well as the possibility of reading on a Solaris/Indiana machine. Anyone have the resources to test?

	When you give ZFS the whole disk, it writes an EFI-like label on the drive and makes us of one partition for the ZFS data. So there *is* a form of partitioning at the lower most layer, it is just *not* user managed partitioning.

--
Paul Kraus
Deputy Technical Director, LoneStarCon 3
Sound Coordinator, Schenectady Light Opera Company