[zfs-discuss] Re: Very newbie question
strntydog at gmail.com
strntydog at gmail.com
Thu Oct 24 02:05:43 EDT 2013
>>> 1. ... system that has *only* ZFS drives.
The system will be very stable and run fine after boot. The problem isnt
ZFS per-se. but grub2's ZFS implementation, which is not the same as ZoL
and is not as reliable, or as well tested or as feature complete.
I can personally attest that during zfs upgrades or grub2 upgrades its
always a "cross the fingers" scenario for me when rebooting. Sometimes it
works fine, sometimes I am hosed and trying to get it booting using grub
It sub optimal, but what i now do is put a cheap usb thumb drive in a usb
holes and use it for /boot with ext2. It should be possible to use 2 thumb
drives and have a /boot and /boot2 if you really need mirroring on it. I
only do this so that when i feel comfortable with gub2 stability i can just
go back to native zfs boot. Its painless and works reliably.
For me, some or all of this may relate to 2 below but i don't know for sure.
>>> 2. I have read that one should give ZFS the entire drive(s), ,,, What
penalty does one pay for placing partitions rather than entire drives under
Potentially a very heavy one. If you layout your partitions in a bad way
it can totally confuse zfs. This happened to me and i now have to rebuild
a server because the pool became unrecoverable after zpool became
hopelessly confused. What happens is if you have a partition which ends at
the end of the drive, and it contains zfs metadata, zfs will not reliably
be able to determine if the true "whole drive" (/dev/sda) is the zpool
device or if its just the last partition (/dev/sda2) which contains that
metadata. When that happens on import zpool will fail because it says the
pool devices are faulted. I had this happen to two seperate machines, and
it is the same under ZoL as illumos (which i tested). A simple
"workaround" to force an import is to make a "/dev/disk-by-parts" which
only has partitions in it and not full devices and then tell zpool to use
that with '-d'. That works, but you cant have that at boot, and so things
get bad when you reboot, it will also probably fail if its a secondary pool
when zfs tries to 'mount -a' during booting. If you must make your own
partitions, make sure the last physical partition on the drive is NOT a zfs
The 8MB partition Zpool makes when giving it full devices eliminates the
possibility of Zpool confusing a partition from a whole device containing
zfs. I think thats one of its main purposes.
On Wednesday, October 23, 2013 7:33:20 AM UTC+8, D. R. Evans wrote:
> I apologise for the basic nature of this question (or, more accurately,
> questions). I've read as much as I can find about ZOL, and have become
> increasingly confused rather than enlightened.
> 1. I have read that it is either (a) difficult; (b) unreliable, or (c)
> impossible to have Linux running on a system that has *only* ZFS drives.
> What's the truth?
> The basic problem here seems to be the one of booting directly off a ZFS
> drive. Can this actually be done reliably? If so, where are there some
> (FYI, I'm currently using Kubuntu.)
> 2. I have read that one should give ZFS the entire drive(s), not
> just partitions on the drive(s). But other advice (particularly
> ignores this and tells me to partition the drives so that there's a
> non-ZFS boot partition in addition to a ZFS partition where everything
> resides. What penalty does one pay for placing partitions rather than
> drives under ZFS control?
> The "simple" solution that seems to be most frequently proposed is to use
> for everything except /boot. But that doesn't seem to be particularly
> since it means that one needs to go through the relative pain of using
> something like Linux software RAID for the /boot partition. One important
> reason that I'm looking at ZFS is to try to get away from the relative
> pain of
> configuring and managing Linux RAID (I realise there are other very good
> reasons for preferring ZFS, but if I can't escape Linux RAID completely
> and I
> have to use RAID for /boot, then I might as well just stay with with my
> current functioning ext3-on-RAID configuration).
> I hope that I'm being sufficiently clear in the midst of my confusion.
> Doc Evans
> Web: http://www.sff.net/people/N7DR
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