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Re: poor raid5 performance of 3ware 7500 under Linux



   1. poor raid5 performance of 3ware 7500 under Linux (Alex V. Verbitsky)
   2. Re: poor raid5 performance of 3ware 7500 under Linux (Samuel Flory)

I am experiencing a poor sequental write performance with 3-disk RAID5
array on 3Ware 7500-8 - it is only 11-12 MB/s. Under Win2000 i get 30-35 MB/s
from the same array.

Has anybody managed to get good (> 30 MB/s) raid 5 write performance
from 3ware 7500 on Linux and desktop (non-server) hardware - 32-bit
33MHz PCI ?

If you are using a 3Ware card under Linux, you might as well use software RAID. It is reliable, more flexible,, and a LOT faster.
It is a pity you have to use a motherboard with a 32bit PCI slot.
I infer this from you saying "32-bit 33MHz PCI"


One thing to watch out for is that it is easy to get amazingly good performance on a benchmark by using a block write size smaller than system memory.
When we benchmark we run the tests with writes set to a size at least double the physical RAM in the machine. This is more likely to be accurate.
When we ran the tests using 512M block size we get sequential writes around 45MB/sec.
When we used 4MB blocks, it dropped down to around 34MB/sec


Anyway, if you want a better solution, grab mdadm from Neil Brown.
It is available at
   http://www.cse.unsw.edu.au/~neilb/source/mdadm/
and
   http://www.{countrycode}.kernel.org/pub/utils/raid/mdadm/

Anyway, using that, a 3Ware card, on a 32 bit PCI slot on an NForce2 motherboard with an AMD Athlon XP2500, I see for performance on a 4 disk RAID5 set for sequential block writes between 33 and 40MB/sec, using Seagate (33MB/sec) and WD drives (40MB/sec)

I can email you the full report separately if you are interested.



With our best regards,

Maurice W. Hilarius       Telephone: 01-780-456-9771
Hard Data Ltd.               FAX:       01-780-456-9772
11060 - 166 Avenue        mailto:maurice harddata com
Edmonton, AB, Canada      http://www.harddata.com/
   T5X 1Y3




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