Re: Advice sought on moving to AMD64
On Mon, Jun 20, 2005 at 04:01:20PM -0400, Nathan Dragun wrote:
> So, why not get SCSI that supports the same thing?
SATA drives are much bigger, often have higher transfer rates (although
slower seeks too in general compared to 15k drives), have nicer cables
that don't block airflow, cost much less as does the controller, and a
nice scsi raid card also costs much more than an SATA hardware raid
card. With SATA hardware raid you get much more space and usually more
speed for a lot less money.
> Ah, didn't know about that one actually, havn't researched SATA drives
> being manufactured in a while.
Up until the last 6 months or so they were all using IDE to SATA
converter chips instead, but now they are doing native SATA instead.
> Thats what SCA is for. Easy to adapt into any SCSI system even if it
> does not defaultly support SCA with a $5 adapter. I've never had a bad
> drive ever take down the channel.
Well if that works, that's good. It wasn't part of the scsi spec
itself. Anyone putting two drives on an ide connector are also asking
for trouble of course while one per cable is fine.
> So you've got my interests in SAS. What kind of system is it exactly?
> Targeted market? Compatibility? Expected release? I'm thinking a search
> on google for 'SAS' would give me a lot of what I'm not looking for. lol
SAS = Serial Attached SCSI.
nice features are:
Dual ported drives: Makes it easy to connect a drive to redundant
controllers
Bus expanders: Essentially switches for drives. Connect a bus expander
to a SAS port and then connect drives or more bus expanders to the ports
of the bus expander. Way more than 7 or 15 drives per connector that
way. Two bus expanders connected to the dual ports of a pile of drives
and to two controllers could make a rather robust setup with many
drives. I believe the number of drives within a single domain is in the
thousands. Might have a throughput problem though if you have too many
drives going into a single controller port, but then again, sometimes
throughput isn't what is required.
SATA drive support: A single SATA drive can be connected to any SAS
controller port. Can not be connected through bus expander though.
SATA to SAS converters are however likely to exist to assign an id to an
SATA drive so it can be connected to a bus expander. SATA drives do not
get dual ports though, so no increased reliability with SATA drives.
Initial speed is 3Gb/s (same as SATA version 2). Later 6 and 12 are
going to be released.
Of course like SATA the connector is designed for hotplug operation.
There are also external connector versions of the port, unlike SATA.
I expect prices to be just as scary as for parallel scsi. Devices are
expected to ship this year.
http://www.serialattachedscsi.com/
Len Sorensen
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