The Deliverator – Wannabee

So open minded, my thoughts fell out…

All Hail SCSI, The Once and Future King?

Posted by Deliverator on December 30th, 2005

There really is a lot of great server hardware coming to market at very cheap prices. I picked up a brand new (still in original antistatic bag) 15K RPM SCSI hard disk, cabling and Adaptec SCSI controller the other day for only $35. This set up easily outperforms the top of the line 10K SATA “Raptor” HDD, which currently sells for around $200. With a dual channel Ultra 160/320 SCSI RAID controller and four 15K RPM hdd’s one should be able to create a four disk stripe able to move somewhere between 240 and 320 MB of data per second, depending on the access pattern. This is enough to actually saturate a normal PCI bus, so one would need either a 64 bit PCI slot or a newer PCI Express SCSI adapter to really achieve these sort of rates. Is SCSI the once and future king of the desktop?

SCSI:

– Complex, thick ribboned cabling sometimes requiring special terminators or jumpers to be set on drives.
– Expensive client adapter cards
– Scsi drives typically lag far behind EIDE drives in capacity (as they are used in servers where reliability is a bigger concern).
– Easy to saturate the scsi channel from the client adapter to the drives, especially with todays disks that are capable of pushing 60-80 MB/s. Most scsi cards have multiple channels to minimize this problem.
– Easy to saturate the bus architectures (by which the scsi card talks to the rest of the system) found in today’s desktops, although rapid adoption of PCI Express will probably make this a moot point.
-Command QUE reordering has been extant in the SCSI world for a LONG time, just added to SATA in the form of NCQ (more commonly) and TCQ (rarely adopted).

SATA on the other hand:

-Thin point to point cable
-No jumpers to be set EVERY AGAIN – YAY!
-ports on existing desktop motherboards, often with some level of raid support. There are rarely enough for a larger stripe or raid 5 array, however
-300 MB/s of bandwidth available to each SATA device, with latest SATA standard makes it pretty much impossible to saturate the connection between the SATA client adapter and a SATA HDD. With controllers hooked into a Hyper Transport bus, which is even more difficult to saturate.
-SATA HDD’s available in capacities up to 500 GB in 7200 RPM and 74 GB in 15K RPM. SCSI drives have them beat in speed, with 15K RPM 150 GB drives available, but certainly not in overall capacity.
-Lots of cheap 15K RPM (though small 18-36 GB capacity) drives coming onto the used market.

SATA looks to have a very bright future ahead of it, but old SCSI gear may have a last chance for some glory. Of course, hard drives may all go the way of the dodo in 3-5 years (always 3-5 years!) when holographic transdimensional quantum storage makes it possible to store our entire porn collection on the head of a pin – next to the choir of dancing angels, mind you.