Re: How fast should an IO be on a SYMMETRIX?

Hello,

As Jonathan Lewis wrote regarding Symmetrix:

"rate of 10 ms per read is pretty reasonable

for random, non-cached I/O, unless you happen

to have the newest fastest discs on the market"

and

"The numbers I picked out were from the tkprof summary:

    254 disk reads in 2.50 elapsed seconds

    which is 100 reads per second

    which is 10ms per read"

This is rows from the tkprof output:

call count cpu elapsed disk query current

Fetch 33 0.06 2.50 254 736 0

Well, but VC got the following numbers on his home PC with IDE disk:

call count cpu elapsed disk query current

Fetch 2 0.27 0.54 375 376 0

Based upon method of Jonathan Lewis the rate of IDE disk is 1.44 ms per

read.

Who can explain me why IDE disk in 7 times faster than Symmetrix ?

And what is magic value of 10 ms for disk (may be this one is defined by

disk seek time) ?

I doubt that seek time of IDE disk is equal to 1.44 ms.

I agree that apples-to-apples should be compared and database in case of

Symmetrix placed on raw devices but in the case of home PC probably not

and works read-ahead cache but where is Symmetrix cache?

Otherwise, assume that the block size is 8K and as Symmetrics timing

is 10 ms that transfer rate will be equal 800 KB/s.

It seems very slow.

May be the best solution is to move database from HP-UX server and Symmetrix

storage to laptop or home PC with IDE disk ?

--

SL


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