2 Bronze

SAS 5/IR Performance

I have recently purchased two PowerEdge 840's. Each has the internal SAS 5/IR Controller, with 4 x 250GB SATA drives. The config of the disks is two drives are mirrored to boot the OS, and the other two are not raided as the data can easily be restored. Both these machines are installed with Windows 2003 SP1. All the latest drivers are in use.
I have been VERY disappointed with the disk performance. Copying an amount of data ( 8GB sql database, single file) is taking literally 20 mins to copy. The OS becomes unresponsive. Any ideas ?
Replies (18)
4 Tellurium

Hi The Taltos,
  SAS 5/i is not a hardware RAID, it's depending on the O/S to provide the RAID functionality, you're experiancing the reason we offer hardware RAID: to offload handling the RAID arrays to a special purpose processor on the RAID controller.
  Look at your performance monitor you're getting processor bound, you might also want to look at the page file settings
2 Bronze

I disagree.  The SAS *IS* a hardware raid device.  The OS is not doing the raid management.  The problem is the drivers and write-caching.  Write caching is disabled because these cheapy raid cards don't have battery AND RAM on them..thus they are set in write-through mode which is brutually slow. There doesn't seem to be an easy way to enable this write-caching I currently have a ticket open hoping that an engineer at dell will resolve this issue.
What the user is experience is a combination of both the write-through slowness AND windows 2003 starting to page after a few GB of file transfer
Here is a good thread of UNIX guys discovering the issue, and fixing it by enabling Write-Caching:
2 Bronze

I figure out how to enable the write caching without having to run stuff in linix, thank goodness.

To enable write caching on a Dell SAS 5/iR raid controller

Danger: this controller does not have a battery on board to handle cached writes
during an unexpected power outage, that's why they make it hard to set this.

This change makes a massive change in disk performance.  I was copying a 135 MB file from one folder to another to test this.  Before enabling write caching, it took between 25 and 37 seconds to copy this file.  After enabling write caching, it took 5 seconds.  In my case, we can risk the potiental corruption in the case of a sudden power outage.

Download LSIUTIL from lsi.com
Click support and downloads.  Last file is LSIUtil.  Accept their terms and the download commences.

Expand the zip file, run LSIUtil.exe from the windows subfolder.
This opens a dos box.
Select your controller - in my case there was only one.  <1 enter>
Select option 21 - RAID actions.  <21 enter>
Select option 32 - Change Volume Setting <32 enter>
First prompt is the main one:
Enable write caching: [Yes or No, default is No] <Yes enter>
Offline on SMART Data [Yes or No, default is No] <enter> (leaves default)
Auto configuration: [Yes or No, default is Yes] <enter>
Priority resynch: [Yes or No, default is Yes] <enter>
Hot Spare Pools (bitmask of pool numbers): [00 to FF, default is 01] <enter>

Then <0 enter> your way out of the utility (take 3 of them).

I know it's been two years since the prior post, but hopefully it will save someone the hours of searching I spent coming up with this solution.

- Tony

3 Argentum

In this case, “enable write cache” refers to the hard drive cache settings not the controller cache (data-lost on power outage still applies).
The SAS 5/iR does not have any memory to cache data, for which it does not support RAID volumes on Write Back, all RAID volumes on this controller are Write Through.
SAS drives may also help improving performance.
Make sure you are running on the latest FW, version:

2 Bronze

Ah, that makes more sense to me.  I could still see it saying "write through" in OpenManage, but the performance increased 5 to 7 times in my write tests.  I did upgrade all of the firmware including the SAS 5, that made no noticable performance difference (but didn't hurt anything either).

We are using SAS drives on all servers purchased since this one experiment in SATA.

- Tony

2 Bronze

It's a good thing I found this link...I'm having the same issues and would like to make the change..


One question though...Do you have to rebuild the array after making this change, or can it be done on the fly?



2 Bronze

This was a non-destructive change, there was no rebuild required.  Good Luck!

- Tony

2 Bronze

This worked perfectly for me and SOLVED my very SLOW PowerEdge 840 server with SAS 5/iR.  I did have some trouble finding the utility on the LSI site, so here is the actually link as of 9/14/10.

Speed tests showed 100 times faster results after turning on write cache.  No reboot required.  Just need to be aware of the potential problems you could have in the event of a power failure.


2 Bronze

Hi Tony,


Just want to say a big fat thank you for this, i've had a precision 690 for a few years now and it's always been slow with defrags, general access times, and hanging on boot ups etc 


This has just made my work computer fantastic to use, it's like a new machine. 


Just saying thanks for the post, it was certainly helpful - i'm surprised DELL let this machine go out at £1500 with such poor performance. Not impressed with DELL at all! 


All the best




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