I'm a small-time sysadmin with big storage aspirations (I'll be honest
- for a planned MythTV back-end, and *ahem*, other storage), and I've
recently discovered ZFS. I'm thinking about putting together a
homebrew SAN with a NAS head, and am wondering if the following will
work (hoping the formatting will stick!):
SAN Box 1:
8-disk raid-z2 --> iSCSI over GbE >--+
|
SAN Box 2: | NAS Head:
8-disk raid-z2 --> iSCSI over GbE >--+--> N-volume zfs pool --> NFS/SMB
|
SAN Box N: |
8-disk raid-z2 --> iSCSI over GbE >--+
In plain english, for each SAN box, combining 8 (or so) disks in a ZFS
raid-z2 pool, sharing the pool over GbE via iSCSI, then combining it
with other (similar) SAN volumes in a non-redundant zfs pool on the
NAS head, working out the partitioning, quotas, etc there.
I'm coming from a Linux Software RAID point-of-view, and (to me) this
is kind of like a RAID 6+0, with an intermediate iSCSI connection.
Using 200GB hdds in the SAN boxes, I'm looking at (roughly) 3.6TB of
available storage for a 3-SAN box setup as described.
I like the error-correction quality of ZFS; however, the ZFS
Administration Guide states: "A non-redundant pool configuration is
not recommended for production environments even if the single storage
object is presented from a hardware RAID array or from a software
volume manager. ZFS can only detect errors in these configurations."
Does this caveat still apply if the constituent volumes (aka storage
objects) are themselves redundant ZFS pools?
I assume the following:
- Hardware errors in the hdds will be detected and dealt with by the
ZFS raid-z2 pools in the SAN boxes.
- Data added to the topmost ZFS pool will likely be allocated in an
arbitrary fashion over its constituent volumes.
- Compression can be enabled per partition created on the topmost ZFS
pool (on the NAS head).
- Volumes can be added to the topmost ZFS pool as SAN boxes are added
to the network, increasing the overall capacity of the topmost pool.
Would I be better-off at the top-level ZFS pool (at the NAS box) with a
simple RAID 0, instead of the non-redundant ZFS pool?
Please comment as you see fit; let me know if I'm making any
fundamentally inaccurate assumptions. I want to make sure that, when I
implement this, I'm doing the Right Thing.
Thanks in advance.
-Jim
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