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Question about throughput and access time

Last response: in Storage
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April 28, 2010 6:47:13 AM

Hello, I am still somewhat a newbie learning about hard drives, and was hoping some of you may have the answers I may seek.

Currently I am comparing the SAMSUNG Spinpoint F3 HD103SJ 32 MB 1 TB
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

and the WD1001Fals Caviar Black 32 MB 1 TB
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

My question is, I am a little confused about which these two things do, throughput and access time.
From what I understand, access time is how fast it accesses the data, and throughput is how fast it transfers things?

So, should I want faster throughput for if I'm transferring alot of files, and access time is better for loading applications? And to load games faster, would I want better throughput or access time? Thanks

a c 415 G Storage
April 28, 2010 7:14:33 AM

Access time is essentially the time required to FIND a file.
Throughput (usually called "transfer rate") is how quickly a file can be read or written once it's been found.

If you only need to find a few large files and then read them, then transfer rate is most important.

If you need to find lots of small files and read them, then access time is most important.

Access time tends to be more important for booting a system and starting up applications. For games, it depends on the game. Games that have to load large scenery files, for example, would probably benefit most from a drive with a fast transfer rate.
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a c 127 G Storage
April 28, 2010 7:15:23 AM

Sminlal beat me to it. ;-)

throughput = bytes/sec that you can push; mostly when reading/writing large files

access time = seek time; time to find files (5-20ms)

Another important spec is IOps. Access time only relates to a single queue depth; IOps would be like a stream of random I/O. While access times do not scale with RAID, IOps does.

So the three performance specs (throughput, access time and IOps) are all related in some way. For your system disk, the latter two are more important than throughput; for a download disk that stores only large files throughput is the only thing important.
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April 28, 2010 4:14:02 PM

Ah, thank you for the response. I did not know some games would continuously read off the hard drive. I thought the hard drive basically loads up the map (load time) and then passes it off to the ram afterward. So with the Samsung, the throughput is better, but the access time is better on the WD Cavier black. Which do you think would be more important? Also, I am assuming IOps is Input/Output. So in raid configuration, access time does not scale. So if I was to do raid 0, would it be better to get two drives with a faster access time, but slower throughput? That way throughput is still increased while I cannot change the access time speed?

O and a question on the cache. I notice there is 64MB, 32MB and so on for cache. Cache is just where things that are used more often is generally in cache, and it is faster memory. What exactly does the cache do for the hard drive? Is it a big difference between 64 MB and 32 MB or even 16 MB? I notice like a velociraptor will have 10000 RPM, but on 16 MB cache. Whereas a WD cavier black is 7200 RPM with 32 MB cache. Thanks
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a c 415 G Storage
April 28, 2010 6:11:01 PM

Drives having access times and transfer rates that are within, say, 10 to 20% of each other aren't really going to result in much of a noticeable performance difference.

For most general-purpose use it's better to buy a drive with the fastest access time, since that improves the performance of booting and starting applications, the thing that people usually spend time waiting for. This is why SSDs (with a 100X faster access time than most hard drives) perform so well.

Differences between cache sizes are pretty minor. The manufacturers usually include enough cache to buffer a certain number of tracks, and beyond that you won't really see any noticeable performance gains.
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