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Performance problem with SATA2 hard drive on dell poweredge SC1425

Hi everybody,

we just change our scsi hard drive by a sata2 one (SAMSUNG HD103UJ) on a dell poweredge SC1425 server. This

server OS is a debian lenny distribution (2.6.26-2-686 kernel)

We use this server as a virtualization server but it is now very slow. It looks like the hard drive performance are quite poor :

Write

------------------------------

bigfish:/tmp# dd if=/dev/zero of=/virtual-machines/testhd bs=4096 count=131072
131072+0 records in
131072+0 records out
536870912 bytes (537 MB) copied, 57.6279 s, 9.3 MB/s

------------------------------

Read :

------------------------------

bigfish:/tmp# hdparm -tT /dev/sdb
/dev/sdb:
 Timing cached reads:   1692 MB in  2.00 seconds = 845.72 MB/sec
 Timing buffered disk reads:  104 MB in  3.02 seconds =  34.42 MB/sec

------------------------------

 

However it looks like the drive is recognised as a SATA2 drive as we can see on dmesg :

[    7.782438] ata2.00: ATA-7: SAMSUNG HD103UJ, 1AA01118, max UDMA7
[    7.782438] ata2.00: configured for UDMA/133

Thanks very much for any help !

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4 Replies
Dev Mgr
5 Rhenium

Re: Performance problem with SATA2 hard drive on dell poweredge SC1425

There may be a configuration, driver or hardware issue, but in general:

 

When virtualizing (running multiple virtual machines), harddrive speed becomes very important as instead of just 1 OS with it's applications, multiple OSes and their multiple applications are accessing the disk subsystem.

 

As most SCSI drives are significantly smaller than SATA drives, it's also not unlikely that you put even more VMs on the disk, generating even more (random) IO, which means even more of a hit on the slower drive.

 

I'd suggest to consider going SAS (15k rpm if you can afford it), Western Digital's Velociraptor (10k rpm SATA available up to 300GB), or go raid 10 (raid 5 isn't the best choice when running a decent number of VMs) with 4 or more SATA drives.

Member since 2003

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Re: Performance problem with SATA2 hard drive on dell poweredge SC1425

Thanks very much for your answer.

You're absolutely right but performances are bad even when no vm is running. Here is the

HD results when no vm is running :

bigfish:~# dd if=/dev/zero of=/virtual-machines/testhd bs=4096 count=131072
131072+0 records in
131072+0 records out
536870912 bytes (537 MB) copied, 48.8584 s, 11.0 MB/s
bigfish:~# hdparm -tT /dev/sdb

/dev/sdb:
 Timing cached reads:   1588 MB in  2.00 seconds = 793.41 MB/sec
 Timing buffered disk reads:  110 MB in  3.09 seconds =  35.61 MB/sec

It looks like is is quite low ...

Thanks again for any help.

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Dev Mgr
5 Rhenium

Re: Performance problem with SATA2 hard drive on dell poweredge SC1425

I'd suggest to download a different distro and use a live-cd or so and see what kind of performance a different distro can get. Ubuntu's desktop install CD is a live CD, but there are other options like Knoppix and such.

Member since 2003

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Rodgek195
1 Nickel

Re: Performance problem with SATA2 hard drive on dell poweredge SC1425

Hi, I have found the very same thing.

If you look at the Raid card advanced settings you will probably find even though it has seen the drive as a SATA2 drive it connects at a SATA1 speed of 1.5gbs

I have managed to increase the speed of the drive with the help of a interposer card and using Samsung drives or Seagate, Never use WDigital in the Dells something i have learned. simlar problem as the HP servers.

I also noticed that the drive speed does not seem to change even with a SAS5i card to a PERC5 512mb cache either so its not the raid card thats slowing it down. I replaced the Backplain and still no change but yet i have a identical server Dell 1950III that runs the drives fine at 3gb/s

I have checked all the Bios Levels and even tried swapping parts from 1 server to the other to see if i could find out why. but i have not had any luck yet.

The only diference in the servers i have is 1 server is a QC2.66 server and the other is a QC2.26 server its the 2.26 that runs the disks slow and the 2.66 runs them fine with no problem.

I even been looking to see how i can mod the server and add a SATA3 PCI X card but its getting the cables to the drives thats the problem and then I have probelm of no power either  so if i manage to mod the server correctly and get it working i will let you know.

 

 

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