SCSI drives recommendations

andrew at andrew at
Tue Jan 22 10:46:56 EST 2002

On Tue, 22 Jan 2002, Steven Hanley wrote:

> I dont know that the calculation of parity is a slow down, I notice that when
> you insmod the raid5 module it does some tests with different code to see what
> speed it can do the parity calculations at.

Theory is good, and in theory, there is no difference between theory and
practice - but in practice, there is.
-- attribution forgotten, sorry :)

I've played around with various raids on my (ide) system at home.  3 fast
ide disks in there (each gets about 33MB/s read).  raid 0 (striping only,
no redundancy) across 2 of them gave me 66MB/s - no slowdown at all.
That's whay I'm currently using.

Now, those 2 disks are 60G each and empty.  The third disk is smaller,
and also has my root partition on it, so I couldn't just try raid 5
without losing lots of capacity.  Still, I wanted to play around with raid
5 and see how it performed, so I used a spare couple of G from the third
disk, and set up a small raid 5.  I only got about 15 MB/s read from it -
less than 1/4 of what it "should" have been.

As I have no real need for redundancy at home (and only 2 disks to use
for it anyway), I just run with raid 0.


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