Hi Loic,
I'm planning to buy a handful (8 to 16) x4500's a bit later this year, so
I am quite interested in the details.
All RAID operations are done in software by ZFS (which acts as both a
filesystem and a volume manager).
ZFS has a "scrub" command that does a background scan of a pool (a set
of disks), it's not done automatically by default but can be automated
very easily.
The "scrub" also verifies the parity/checksum of the data blocks.
There is a example of this in one the ZFS demos on the OpenSolaris web
site: <http://www.opensolaris.org/os/community/zfs/demos/selfheal/>.
Nice demo!
The data found to be damaged during a "scrub" is corrected/repaired
(immediatly) using the various parity/checksum/mirror information
available (see the "zpool" man page on the OpenSolaris web site).
ZFS also has more redundancy than just RAID-5 or RAID-6 (when using
"raidz2" in the latter case), especially in the newer ZFS versions.
The "ditto blocks" for instance, allow you to have multiple copies of
the same data or metadata.
In a system with 24 x 500 GB disks, I would like to have usable storage of
20 x 500 GB and use the remaining disks for redundancy. What do you
recommend? If I understand correctly I can't boot from ZFS so one or more
of the remaining 4 disks might be needed for the OS.
Another nice feature is the "parity check on read" (similar to what DDN
disk controllers do).
I am not a Sun employee or share holder, we just have many X4500 (soon
more than 100, probably around 130 at the end of the year).
We've had X4500s in "production" for almost a year and they have
proved to be very reliable, very fast and globally pretty cheap.
I have heard similar reports from my collaborators at a few other
locations.
Cheers,
Bruce
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