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Unable to enable Write-Caching on Windows 7 x64

Posted on 2013-01-14
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Last Modified: 2013-01-22
This is bit of an odd one. I have a lab server that wasn't getting the Write performance that I would expect. (Based on tests with HDtune) The Controller itself states that Write-Caching is set to enabled. However the OS states that it is not and cannot enable it for the disk.

I also have a 3ware 9550 controller installed with a RAID 5 array and it allows caching to be enabled on the controller and within the OS just fine.

I took an image of the partition on the RAID 10 Array and then blew it away. I recreated the Array making sure that write cache was enabled upon creation. Same Behavior.


The system spec's are as follows:

Motherboard: X7DAE
http://www.supermicro.com/products/motherboard/xeon1333/5000x/x7dae.cfm

SAS Raid Controller: Adaptec 4800SAS with attached Battery Backup
https://www.adaptec.com/en-us/support/raid/sas_raid/sas-4800/

Array: 4 x 15K SAS in RAID 10 - 256k clusters


Windows 7 Pro x64


See attached to see the screenshots from the controller and the OS. I would deduce that enabling and controlling write-caching on the controller would then prevent one from doing the same within the OS. But as I said this is not the case on the 3Ware (LSI) controller.

So shouldn't I be able to modify the write-caching policy of the Disk from the OS? Or is this specific to to Vendor / Driver?
Logical-disk1.JPG
Logical-disk2.JPG
disk0.JPG
windows.JPG
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Question by:EagleMed-IT
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Assisted Solution

by:andyalder
andyalder earned 600 total points
ID: 38777833
In general the OS has no control over the write cache on a RAID controller, some disable the option to set it like your adaptec card and others just ignore the setting under Windows. You can test that with your 3ware card, performance should be the same whether Windows has the cache setting on or off so long as it is turned on via tyhe controller management software.

The write cache on your adaptec is temporarily disabled, is there a problem with your battery? It may just have been flat when you took the screenshot or it may have failed and need replacing.
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Author Comment

by:EagleMed-IT
ID: 38780139
The battery was actually just installed last week and took a few days to fully charge. The thing that bothered me was that even on the controller the MODE says disabled, but the write cache setting says ENABLED w/battery. The controller reports no issues with the battery (optimal) @ 100% charged.

Changing the write cache SETTING on the controller shows no different result when testing with HD tune. Write cache ENABLED or DISABLED yield the same stats.

That leads me to believe that the MODE is critical here. Even though I have the setting @ write cache enabled with battery, the controller is still running with cache mode = disabled.


I tried using the controller command line tool to force the mode to WB (write back) but it says its already configured this way.
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Expert Comment

by:andyalder
ID: 38780425
and if you use arconf getconfig al does it show as temporarily disabled same as the GUI? It may just be a bug and needs a power cycle to realise the battery's charged or simply disabling and enabling (but I think you've tried that).
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Author Comment

by:EagleMed-IT
ID: 38780524
Thanks for the replies andy. Your command sent me in the right direction, its actually:

ARCCONF GETCONFIG 1 AL

I exported the config and as you can see it does show the same as the GUI. I may need to see if Adaptec can provide insight into this, though I'm not entirely sure they will offer support on it.
4800SAS.txt
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by:andyalder
ID: 38780612
With the disks set to write-back I'm surprised it even bothers about reporting the battery status since data loss will occur on sudden power loss regardless.
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Author Comment

by:EagleMed-IT
ID: 38780748
I believe the controller set the disks to WB but I can manually set them to WT if you think this is highly risky. Its mainly test storage for iSCSI Datastores.
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Expert Comment

by:andyalder
ID: 38780960
If it's just test you can pull out all the stops, but enabling the disk write cache by setting them to WB means the disk will tell the controller the data is committed when it is only in the disk cache.
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Accepted Solution

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EagleMed-IT earned 0 total points
ID: 38790414
This is isn't technically resolved but I am going to close it for now. I will reopen if a solution is found.
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Author Closing Comment

by:EagleMed-IT
ID: 38804846
Not resolved but no new information can be provided at this time.
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