Oatway, Ted wrote:
Thanks for the response Richard. Forgive my ignorance but the following
questions come to mind as I read your response.
I would then have to create 80 RAIDz(6+1) Volumes and the process of
creating these Volumes can be scripted. But -
1) I would then have to create 80 mount points to mount each of these
Volumes (?)
No. In ZFS, you create a zpool which has the devices and RAID configurations.
The file systems (plural) are then put in the zpool. You could have one
file system, or thousands. Each file system, by default, will be in the
heirarchy under the zpool name, or you can change it as you need.
2) I would have no load balancing across mount points and I would have
to specifically direct the files to a mount point using an algorithm of
some design
ZFS will dynamically stripe across the sets. In traditional RAID terms,
this is like RAID-1+0, RAID-5+0, or RAID-6+0.
3) A file landing on any one mount point would be constrained to the I/O
of the underlying disk which would represent 1/80th of the potential
available
It would be spread across the 80 sets.
4) Expansion of the architecture, by adding in another single disk
array, would be difficult and would probably be some form of data
migration (?). For 800TB of data that would be unacceptable.
It depends on how you do this. There are techniques for balancing which
might work, but they have availability trade-offs because you are decreasing
your diversity. I'm encouraged by the fact that they are planning ahead :-).
Also, unlike a traditional disk array or LVM software, ZFS will only copy
the data. For example, in SVM, if you replace a whole disk, the resync will
copy the "data" for the whole disk. For ZFS, it knows what data is valid,
and will only copy the valid data. Thus the resync time is based upon the
size of the data, not the size of the disk. There are more nuances here,
but that covers it to the first order.
-- richard
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