HDD question

[donnato]

Hello folks, in my continuing quest for knowledge I`ve come across a spec that got me curious. When comparing HDDs...how important is latency...what is it and , what are some good specs? Thanks all...

[DsoS]

The lower the number the faster the drive is to locate a section on the drive. Basically latency is a delay. You want the number as low as possible. (info is correct, if I recall correctly)

edit:

Found this out on the net...

Hard drive latency is the time that it takes a hard drive to load information from a sector

Edited December 24, 2011 by DsoS

[_echo]

I cant say for sure, as ive really ever only looked at the storage space on platter drives, but I would assume its the same concept as network. The average time it takes from your command to reach the drive.

IE this drive: http://www.newegg.com/Product/Product.aspx?Item=N82E16822148736

Has a 4.16ms latency, so me thinks it means it takes 4.16ms for the drive to respond to read and write requests.

Edit: What DsoS said...

[donnato]

Ah I understand that. Thankyou. I`ll bet also thaqt the lower the latency the higher the price..

[HeyYou]

Ah I understand that. Thankyou. I`ll bet also thaqt the lower the latency the higher the price..

Yeah, that's usually how it works.

Another factor to consider is Cache size. 8mb is too small, 16 is adequate, 32 is good. What cache does is, when you write to a drive, it will fill cache first, which is as fast as the bus speed, then, from cache it will actually write the info to the drive. (which is a slower process.) Same with reads. You request a file, and the drive tells you to stuff it.. No, wait, that's not right...... You request a file, the drive searches it out on the disk, puts it into cache, and then from cache it goes to the system bus. Yeah, that's it.

[donnato]

wow, thanks HY...Which bus is this? CPU...? Does the RAM have it`s own bus..?...I ask because I`m trying to understand clocking speeds...

[_echo]

Probably the speed of the data bus.

Basiucally everything connects to the north bridge, so every wire leading to and from there is its own bus. It can get very complicated and is rather unimportant to the vast majority of users.

[vometia]

Yeah, that's usually how it works.

Another factor to consider is Cache size. 8mb is too small, 16 is adequate, 32 is good. What cache does is, when you write to a drive, it will fill cache first, which is as fast as the bus speed, then, from cache it will actually write the info to the drive. (which is a slower process.) Same with reads. You request a file, and the drive tells you to stuff it.. No, wait, that's not right...... You request a file, the drive searches it out on the disk, puts it into cache, and then from cache it goes to the system bus. Yeah, that's it.

Write-caching makes me twitchy, I usually turn it off since it can cause nasty filesystem corruption (though I suspect NTFS is less prone to this than some); Native Command Queueing is as fast only without the risk, at least if it works the same as SCSI's Tagged Command Queueing. But a big cache is still useful for read-caching, and drives can still be quite intelligent about pre-caching stuff you're likely to want next, such as with big sequential reads.

[donnato]

Again, thank you all so much. I`m beginning to get a clearer understanding of how this all works.