Peter Rival wrote:
I don't like to top-post, but there's no better way right now. This
issue has recurred several times and there have been no answers to it
that cover the bases. The question is, say I as a customer have a
database, let's say it's around 8 TB, all built on a series of high end
storage arrays that _don't_ support the JBOD everyone seems to want -
what is the preferred configuration for my storage arrays to present
LUNs to the OS for ZFS to consume?
Let's say our choices are RAID0, RAID1, RAID0+1 (or 1+0) and RAID5 -
that spans the breadth of about as good as it gets. What should I as a
customer do? Should I create RAID0 sets and let ZFS self-heal via its
own mirroring or RAIDZ when a disk blows in the set? Should I use RAID1
and eat the disk space used? RAID5 and be thankful I have a large write
cache - and then which type of ZFS pool should I create over it?
The only use I see for RAID-0 is when you are configuring your competitor's
systems. Real friends don't let friends use RAID-0.
For most modern arrays, RAID-5 works pretty well wrt performance. While
not quite as good as RAID-1+0, most people are ok with RAID-5. s/-5/-6/g
See, telling folks "you should just use JBOD" when they don't have JBOD
and have invested millions to get to state they're in where they're
efficiently utilizing their storage via a SAN infrastructure is just
plain one big waste of everyone's time. Shouting down the advantages of
storage arrays with the same arguments over and over without providing
an answer to the customer problem doesn't do anyone any good. So. I'll
restate the question. I have a 10TB database that's spread over 20
storage arrays that I'd like to migrate to ZFS. How should I configure
the storage array? Let's at least get that conversation moving...
It almost always boils down to how much money you have to spend. Since I'm
a RAS guy, I prefer multiple ZFS RAID-1 mirrors over RAID-1 LUNs with hot
spares and multiple kilometer separation with multiple data paths between
them. After I win the lottery, I might be able to afford that :-).
More applicable guidance would be to use the best redundancy closest to the
context of the data first, and work down the stack from there. This
philosophy will give you the best fault detection and recovery. Having the
applications themselves provide such redundancy is best, but very uncommon.
Next in the stack is the file system, where RAID-1 and RAID-Z[2] can help.
Finally, the hardware RAID. This begs for a performability analysis [*],
which is on my plate, once things get settled a bit.
[*] does anyone know what performability analysis is? I'd be happy to
post some info on how we do that at Sun.
-- richard
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