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poor raid5 performance of 3ware 7500 under Linux

Hi people,

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.

I have used different methods: dd, iometer and "copy /dev/zero tstfile"
- they all give me the same low figures (11-12 MB/s).

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 ?
And why does Linux give much worse performance than Win2k?
It was disapointing for me to see this after i recommended 3ware cards for
our NAS solution.

3ware use server motherboards and Windows 2k and for their benchmarks.
I found several Linux benchmarks that showed good results but they used server motherboards:

I also found that another Russian guy had the same problem a year ago:

I run RedHat 9 with unchanged kernel and have updated firmware and
drivers to 7.6 version 3Ware software. Write cache is enabled.
Disks used are 80 GB ibm 120gxp (IC35L080AVVA07-0).

I used 2 hardware configurations:
1) Via Epia-M motherboard with C3-933 Mhz, 256MB RAM
2) Asus A7V133 with Athlon 1Ghz, 512 MB RAM
- they showed the same results except for CPU utilization:
on Epia i get high numbers (50-70% for read, 90-100% for write) and
on Athlon numbers are much lower(22-36% read, 7% for write).

I also tested RAID0 3-disk array on Epia (just trying to understand what's
wrong - i need RAID5 for my solution) and get the strange results:
   seq. read (64-1024KB blocks,  1-64 outst. I/O) - 34 МB/s, CPU total 65-70%
   seq. write (64-1024KB blocks,  1-64 outst. I/O) - 48 МB/s, CPU total 100%
file copy (ext2 file system)
   seq. read (cp testfile /dev/null) - 54 МB/s, CPU total 45 %
   seq. write (cp /dev/zero testfile) - 60 МB/s, CPU total 93 %
      [root RH9 3w]# hdparm -tT /dev/sda
        Timing buffer-cache reads:   128 MB in  1.94 seconds = 65.98 MB/sec
        Timing buffered disk reads:  64 MB in  2.00 seconds = 32.00 MB/sec

Under Win2k i get from this array 100 MB/s (66 MB/s at disk end) read and 61 MB/s
write with much lower CPU usage.

Thanks in advance for any help,
sorry for my poor English.

Best regards,
 Alex                          mailto:alexver5 mail ru

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