SATA or SCSI drives - Multiple Read/write speeds.
hahn at physics.mcmaster.ca
Mon Dec 8 21:44:14 EST 2003
> > | My concern is regarding multiple disk read/writes. With IDE, you can
> > | wait for what seems like hours while data is being read off of the HD.
> > nah. it's basically just a design mistake to put two active PATA disks
> > on the same channel. it's fine if one is usually idle (say, cdrom or
> > perhaps a disk containing old archives). most people just avoid putting
> > two disks on a channel at all, since channels are almost free, and you
> > get to ignore jumpers.
> So, admitting my near total ignorance about SATA and whether or not I
> should lust after it, does SATA perpetuate this problem, or is it more
> like a SCSI daisy chain, where each drive gets its own ID and there is a
> better handling of parallel access?
no, or maybe yes. SATA is *not* becoming more SCSI-like: drives don't
get their own ID (since they're not on a bus). in SATA-1 at least,
the cable is strictly point-to-point, and each drive acts like a separate
channel (which were always parallel even in PATA). basically, master/slave
was just a really crappy implementation of SCSI IDs, and SATA has done away
with it. given that IO is almost always host<>device, there's no real value
in making devices peers, IMO.
yes to concurrency, but no to "like SCSI" (peers, IDs and multidrop).
> extra controller (or two). One cable per disk if you use one disk per
one cable per disk, period. this is sort of an interesting design trend,
actually: away from parallel multidrop buses, towards serial point-to-point
ones. in fact, the sata2 "port multiplier" extension is really a sort
of packet-switching mechanism...
> There is also a small price premium for SATA, although admittedly it
> isn't much. So, in your fairly expert opinion, is it worth it?
my next 8x250G server(s) will use a pair of promise s150tx4 (non-raid) 4-port
sata controllers ;)
I don't see any significant benefit except where you need lots of devices
and/or hotswap. well, beyond the obvious coolness factor, of course...
though come to think of it, there should be some performance, and probably
robustness benefits from Jeff Garzik's clean-slate approach.
regards, mark hahn.
Beowulf mailing list, Beowulf at beowulf.org
To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
More information about the Beowulf