How important is hard disk cache/buffer?

How important is hard disk cache/buffer?

Post by Richard Kilgo » Fri, 17 Feb 1995 02:06:50

I need to know if I should be worried with an 850MB hard drive
that only has 64KB of cache.  It is a Western Digital 2850, 850MB,
"average access time" 10ms, and it supports EIDE, but it only has
64KB of cache.  Should I take it back and get a different one?


        - rick

Richard B. Kilgore
Grad Student, University of Texas at Austin


1. hard disk throughput: important factors?


I have four hard disks (IDE) which were not running with DMA turned on (i.e., they were all running in "default 16-bit").  For purposes of this post, they are:

HD1 = Maxtor 2GB
HD2 = Maxtor 4GB
HD3 = Maxtor 55GB
HD4 = Maxtor 10GB

(I don;' really have a fondness for Maxtor; three of the drives were in computers I bought, but I did buy the 55GB one).

Anyway, I ran 'hdparm -t' on each, the the results were:

HD1: ~2.5 MB/sec
HD2: ~3.5 MB/sec
HD3: ~1.75 MB/sec
HD4: ~28.0 MB/sec (yes, I was surprised at this as well; I ran it three times, just to make sure!

After running 'hdparm -c 1 -d 1' on each, the results of 'hdparm -t' are now:

HD1: ~7.5 MB/sec
HD2: ~14.5 MB/sec
HD3: ~2.25 MB/sec
HD4: ~28.0 MB/sec (I didn't really expect it to change very much)

My biggest disappointment was with HD3 (the 55GB), particularly since I had bought it specifically for use in a "digital VCR" application.  As the subject of this post suggests:

  1. Are there any factors that I am able to control (beyond turining DMA on, which I've already done) to increase throughput on HD3 (I'd even be happy with ~5MB/sec throughput).

If there is any further information you would need from me to make this determination, please let me know, and I will do my best to get it for you.


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