On 8/4/2010 10:10 AM, Emmanuel Noobadmin wrote:
>
> derivative work or something along those lines.
>
>> the OpenSolaris or NexentaStor versions since you wouldn't be using much else
>> from the system anyway.
>
> If I really have to, but I was hoping I wouldn't need to learn another
> relatively similar OS and get myself confused and do something
> catastrophic while in console one day. Especially since I'm way behind
> schedule on picking up another programming language for projects my
> boss wants me to evaluate.
That's sort of the point of nexentastor which gives you a web interface
to manage the filesystems and sharing since you don't need anything
else. But the free community edition only goes to 12 TB. That might be
enough per-host if you are going to layer something else on top, though.
>> Snapshots and block-level de-dup are other features of zfs - but I think
>> you'll lose that if you wrap anything else over it. Maybe you could overcommit an
>> iscsi export expecting the de-dup to make up the size difference and use
>> that as a block level component of something else.
>
> Honestly, I've no idea what all that was about until I go read them up
> later although I understand vaguely from past reading that snapshot is
> like a backup copy
It is good for 2 things - you can snapshot for local 'back-in-time'
copies without using extra space, and you can do incremental
dump/restores from local to remote snapshots.
> However, in my ideal configuration, when a VM host server dies, I just
> want to be able to start a new VM instance on a surviving machine
> using the correct VM image/disk file on the network storage and resume
> full functionality.
The VM host side is simple enough if its disk image is intact. But, if
you want to survive a disk server failure you need to have that
replicated which seems like your main problem.
> Since bulk of the actual changes is to "files" in the virtual disk
> file, having snapshot capabilities on the underlying fs doesn't seem
> to be useful. ZFS checksum ensuring that all sectors/inodes of that
> image file are error free seems more critical. Please do point out if
> I am mistaken though!
If you can tolerate a 'slightly behind' backup copy, you could probably
build it on top of zfs snapshot send/receive replication. Nexenta has
some sort of high-availability synchronous replication in their
commercial product but I don't know the license terms. The part I
wonder about in all of these schemes is how long it takes to recover
when the mirroring is broken. Even with local md mirrors I find it
takes most of a day even with < 1Tb drives with other operations
becoming impractically slow.
--
Les Mikesell
lesmikesell at gmail.com