SATA/SSA/SCSI/iSCSI

[Mike]

What's the difference in all these? I've used SCSI and SSA for
a long and am happy with SSA. I'm trying to convince management
to get me (the company) a big thing like the DS4500, but I'm
confused just where SATA fit into the big picture.

Is SATA to be the next, big storage interface/protocol?

Mike

[Markus Baertschi]

Hi Mike,

Here my take on these:

- SATA: Serial ATA, the successor of ATA/IDE in PC space
Used on some low-cost SAN units
- SSA: The (IBM proprietary) precursor of FC-AL
Replaced slowly with FC-AL disks in your SAN box
- SCSI: Good old SCSI
Refusing to die, still used in many disk subsystems
- ISCSI: SCSI over IP
Looks interesting, has not caught on (yet ?)
- FC: FibreChannel (You didn't mention this one)
The interconnect you use to connect your SAN box containing
the FC-AL drives to your servers.

Your DS4500 (FastT 900) has eight FC ports to connect
servers and eight FC-AL ports to connect disk drawers.
If you choose EXT700 drawers you populate them with up
to 14 FC-AL high-performance disks. If you choose ETX100
drawers you fill it with SATS low-cost disks. Sort of
the best of both worlds.

Markus

[Christopher D. Clausen]

Markus Baertschi wrote:
> - ISCSI: SCSI over IP
> Looks interesting, has not caught on (yet ?)

iSCSI is pretty useful and cheap. I accquired some older (PII, PIII)
x86 machines without hard disks and bought some $2 Intel bootable
network cards and now I have several of them running GNU/Linux over
iSCSI without a local disk. Details at:
https://www-s.acm.uiuc.edu/wiki/space/iSCSI

There are various vendors that sell iSCSI SAN solutions, Equallogic
looks the most promising. There is a rudimentary review of various
iSCSI software / hardware vendors linked to from the above URL.

I've had some problems trying to find iSCSI initiator software for AIX,
but I believe that Cisco has it available with purchase of the Storage
Router (SN 5400 series) products. I think IBM also have some iSCSI
initaitor software available, but its not draft 20 compliant. IBM does
sell iSCSI equipment, but its out of our price range. I would assume
IBM's initiator works with their iSCSI hardware products, but this
should probably be tested thoroughly first.

iSCSI should enable some cheap (under $50,000 USD) SAN solutions once
the market gets going and prices drop. iSCSI HBAs are about $600 right
now, and an HBA is currently the only way to boot Windows over iSCSI
(Cisco has a solution, but it doesn't work very well.)

Ideally, I'd like to use AIX as the iSCSI host (b/c of superior I/O and
disk management) and use the freely available Microsoft Windows or Linux
initiators to connect, but I cannot seem to find a good, cheap iSCSI
software host for AIX.

Feel free to email me directly with questions. I enjoy talking about
iSCSI and spent most of the summer evaluating various hardware and
software solutions.

<<CDC
Christopher D. Clausen
ACM@UIUC SysAdmin