How is this possible?

[Careface]

my mate and i were debating what speed SATA150 was, and he told me that his SATA drive read at over 1GB/sec. i was like "dude.. sif" but later on msn he showed me

Michael - adventdesigns says:
/dev/sda:
Timing cached reads: 2656 MB in 2.00 seconds = 1326.88 MB/sec
HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate ioctl for device
Timing buffered disk reads: 186 MB in 3.02 seconds = 61.54 MB/sec
HDIO_DRIVE_CMD(null) (wait for flush complete) failed: Inappropriate ioctl for device


how is this possible? i didnt think that an HDD could read anywhere NEAR that amount per second.. my sata certainly doesnt. any thoughts?

Careface*

[emboss]

Important words here are "cached" and "buffered". For cached, it's not measuring transfer rates to and from the disk, or even across the HDD interface, but rather how fast the OS can satisfy requests out of the (system memory) cache. Basically, it's the system memory bandwidth divided by two minus a bit for overheads. To point out how useless this number is WRT HDD performance, you could get several gigabytes per second off a floppy disk on a high-end system ...

Buffered reads is a much more realistic test, as that at least is hitting the disk. ~60MB/sec sounds about right for a recentish hard drive.

FWIW, SATA150 is 1500mbit/sec and uses 10-bit encoding per byte, giving a total interface data rate of 150MBytes/sec (note: not MiBytes/sec). You lose a few percent to protocol overheads on top of that.

[Careface]

ah, thanks for that info :) ive been wondering that for a while. i didnt know having things cached made that much difference either O_O

Careface*

[-maddog-]

He may have i ram or solid state, but very unlikely, since solidstate is almost impossible to get and i ram is rarely used (I wouldn't resets if turned off for more than 16hrs, though would make a good temporary storage).

[ocminimus]

Interesting. Nice post emboss.