Saying "Solid State disk" in the storage arena means battery-backed DRAM
(or, rarely, NVRAM). It does NOT include the various forms of
solid-state memory (compact flash, SD, MMC, etc.);"Flash disk" is
reserved for those kind of devices.
This is historical, since Flash disk hasn't been functionally usable in
the Enterprise Storage arena until the last year or so. Battery-backed
DRAM as a "disk" has been around for a very long time, though. :-)
We've all talked about adding the ability to change read/write policy on
a pool's vdevs for awhile. There are a lot of good reasons that this is
desirable. However, I'd like to try to separate this request from HSM,
and not immediately muddy the waters by trying to lump too many things
together.
That is, start out with adding the ability to differentiate between
access policy in a vdev. Generally, we're talking only about mirror
vdevs right now. Later on, we can consider the ability to migrate data
based on performance, but a lot of this has to take into consideration
snapshot capability and such, so is a bit less straightforward.
And, on not a completely tangential side note: WTF is up with the costs
for Solid State disks? I mean, prices well over $1k per GB are typical,
which is absolutely ludicrous. The DRAM itself is under $100/GB, and
these devices are idiot-simple to make. In the minimalist case, it's
simply DIMM slots, a NiCad battery and trickle charger, and a
SCSI/SATA/FC interface chip. Even in the fancy case, were you provide a
backup drive to copy the DRAM contents to in case of power failure, it's
a trivial engineering exercise. I realize there is (currently) a small
demand for these devices, but honestly, I'm pretty sure that if they
reduced the price by a factor of 3, they'd see 10x or maybe even 100x
the volume, cause these little buggers are just so damned useful.
Oh, and the newest thing in the consumer market is called "hybrid
drives", which is a melding of a Flash drive with a Winchester drive.
It's originally targetted at the laptop market - think a 1GB flash
memory welded to a 40GB 2.5" hard drive in the same form-factor. You
don't replace the DRAM cache on the HD - it's still there for fast-write
response. But all the "frequently used" blocks get scheduled to be
placed on the Flash part of the drive, while the mechanical part
actually holds a copy of everything. The Flash portion is there for
power efficiency as well as performance.
-Erik
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
