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Figure 24 shows buffered sequential throughput on both a Quantum Atlas 10K SCSI drive on an Adaptec Ultra160 SCSI controller and a Quantum Fireball 5400 RPM IDE drive connected to a 3ware controller. Despite having half the rotational rate of the Atlas, the Fireball is able to achieve about 80% of the Atlas’s throughput — more than 19MBps. This is due to the Fireball having a higher areal density than the Atlas. Thus, the lower rotational rate of the Fireball is offset by a greater number of bits per inch.
There are no surprises here; the buffered throughput trend lines of the IDE drive are similar to that of SCSI drives.
Both buffered reads and writes showed good performance for all request sizes and are able to achieve disk speed. Particularly good performance was achieved at small request sizes as FS buffering coalesced the requests into 64KB blocks. This allowed the small requests to run at disk speed. The only exception to this rule was the case of 2KB writes where the throughput was slightly less than 5MBps with WCE. This was because for each 2KB write, Win2K reads a 4KB page off disk and then merges the 2KB write with it. The 4KB read before each 2KB write more than doubles the overhead for each request. Even with this additional overhead, buffered 2KB writes still offered a throughput advantage over unbuffered 2KB writes. Increasing the depth of buffered requests resulted in minimal performance gains.
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