On Mon, 18 Jan 1999, reschke wrote:
> Check out:
>
> http://beowulf.gsfc.nasa.gov/bds/disks.html
>
> especially the bit at the bottom of the page which shows almost perfect
> scaling across three IDE disks/channels. Using cheap IDE drives in DMA
> mode completely avoids the CPU overhead penalty associated with the old
> PIO-mode divers. I'm currently using two $250 11GB Maxtor 7,200 RPM
> diamondmax drives on the two motherboard IDE channels of an Intel
11GB DiamondMAX? That is probably the 2880 seris...a 5400rpm drive.
Diamond makes the Diamond MAX plus series with sizes up to 10GB that are
7200rpm.
> PR440FX motherboard based system with 256MB RAM and a 300MHz PII.
> Bonnie shows:
>
> -------Sequential Output-------- ---Sequential Input--
> --Random--
> -Per Char- --Block--- -Rewrite-- -Per Char- --Block---
> --Seeks---
> Machine MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU
> /sec %CPU
> 1024 4868 98.5 23951 25.1 9062 27.3 4319 94.6 20137 23.9
> 80.1 1.6
Now if Bonnie was an application that accomplished meaningful work, this
could be useful. Since it doesn't, it just shows the speed of single
read/write stream. Since it buffered through the OS, the first 240MB
or so are written instantly to memory, so you aren't even getting a
meaningful disk perf result either.
> Not too shabby. Compare this to the price/performance of a single 18GB
> SCSI disk.
>
> I believe the bottom line is that SCSI - particularly LVD/Ulra2 SCSI -
> is clearly superior for applications which need tons of disk: SCSI
I disagree. SCSI advantages:
- Higher drive quality. EIDE drives are built cheap, just because that is
what the market buys. Compare the listed MTBF for a Maxtor Diamond MAX to
the list MTBF for a Seagate Barracuda 4LP/XL. In fact, it doesn't seem
that Maxtor publishes MTBF figures...
- Heavy IO. SCSI can have multiple outstanding IO request per bus and per
drive. Most SCSI disks can have to 64 outstanding IO requests. This
allow the host to use overlapping IO to improve performance, and it allows
the drive to re-order requests for faster response. EIDE allows one
outstanding request per channel.
Tom
