On Nov 16, 2008, at 7:15 PM, Danny Carroll wrote:
Eirik Øverby wrote:
I have noticed that my 3ware controllers, after updating firmware
recently, have removed the JBOD option entirely, classifying it as
something you wouldn't want to do with that kind of hardware
anyway. I
believed then, and even more so now, they are correct.
It kinda depends. If there were a good 8 or 16+ port SATA card out
there that *simply* did SATA with no bells and whistles, then there
would be no point buying a Raid adaptor when you want to use things
like
ZFS.
But there are no such cards available.
Allow me to introduce you to Marvell. The sell the SATA controller
used in the Sun thumper (X4500). I've used that same SATA controller
under OpenSolaris and FreeBSD. Unfortunately, that controller doesn't
use multi-lane cables. When you pack in 3 controllers and 24 disks,
it's a cabling disaster.
http://freebsd.monkey.org/freebsd-fs/200808/msg00027.html
Use the RAID-0 disk trick to be able to utilize the controller cache.
And regarding write-back vs write-through; I believe write-through is
equvivalent to disabling controller write cache, however it WILL
cache
the writes in order to respond to future reads of the data being
written. I would guess, but I don't know, that this also goes for
disk-level caches too, though, so it probably doesn't matter.
It is interesting to me that the default setting on the Areca card was
to have the disk caches turned on. I think that is strange because by
default you have a situation that can lead to data loss even if you
have
a battery backup unit.
The Areca cards do NOT have the cache enabled by default. I ordered
the optional battery and RAM upgrade for my collection of 1231ML
cards. Even with the BBWC, the cache is not enabled by default. I had
to go out of my way to enable it, on every single controller.
Matt
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