UNSOLVED
SAS5IR RAID 1 - No write caching, slow performance?
I just got a poweredge 860 and decided to try to save a few bucks by foregoing SCSI drives and purchased 2x160GB SATA drives.
They came configured as RAID 1 however I'm noticing slow performance and notice that write caching is disabled for these drives.
How do I enable it? When I go into the Server Administrator >Storage>SAS 5/iR > Virtual Disks - there are NO Tasks Available.
Read Policy = No Read Ahead
Write Policy = Write Through
I have the latest firmware/drivers
Firmware: 00.10.49.00.06.12.02.00
Drivers: 1.24.04.00
Do I change this outside of windows?
I read somewhere that by default, write caching is disabled on these drives for safety reasons..however, is there no way to force it on? :smileysad:
1626
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Posted June 12th, 2007 13:00
There is no write caching on the SAS 5iR controller.1626
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Posted June 12th, 2007 14:00
>http://lists.us.dell.com/pipermail/linux-poweredge/2007-January/029348.html
>
>I was wondering if you had success in enabling write-caching with this
>controller? I'm in a windows x64 environment and can't find anywhere to
>enable this feature. I understand the controller doesn't have a
>battery however the server is on UPS so I'm willing to take the risk
Yes, I enabled write-caching and I understand this setting on this controller actually enable the write cache of the SATA disks.
Dell told me in future firmware/driver versions this will be done automatically, so I went on with this setting to get back to a normal performance.
To enable write caching I used a Linux command line utility (lsiutil) I found in the Linux driver package I downloaded from Dell site.
I don't know about Windows. If you have ne of those Linux live CD on hand you could boot with that and I could send you the utility.
--
giulioo@pobox.com
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Posted June 12th, 2007 15:00
I believe that Dell is referring to the PERC in this statement. When the original PERC 5I and PERC 5E firmware came out it did not have write-back caching enabled by default. Now, when you create any type of array with the latest firmware, it should enable caching by default.There is no RAM on the SAS 5iR integrated card, therefore there is no write-caching options available. If you look at the features on the PERC it has cache memory and hense the ability to enable caching.1626
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Posted June 12th, 2007 15:00
Nah they're talking about the SAS5/iRBasically you're right..however the work around is to enable write caching on the Hard Disk's themselves which increases performance but carries more risk. My understanding is that if you enable it on the controller, it will enable it for the hard disks as well1626
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Posted June 12th, 2007 17:00
1629
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Posted June 13th, 2007 03:00
As a follow up:PERC5/iR without cache enabled:PERC5/iR WITH cache enabled:1629
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Posted June 13th, 2007 12:00
You say "older version" of the RAID Manager -- that one is dated 04/2007, and does mention SATA write caching specifically in the rel. notes, so it appears to be a fairly recent version of the util. Glad to hear it is the solution though.1629
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Posted June 13th, 2007 15:00
Thanks for all of the information. I ran tests on the SAS 5iR and PERC 5i and came up with very similar performance conclusions.So that everyone is aware, this option is disabled by default because it is not recommended. If you have a system crash you may have a higher chance of data corruption as the disk cache is not battery protected. Windows may also flag events in the system log that the write cache is enabled and data corruption could occur.650
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Posted June 21st, 2007 22:00
The only options are:1) turn on write caching via the Dell Raid Manager tool I linked to. This is *risky* because if your system is not on UPS and you experience a power surge you can potentially lose data. However most will argue that you're in RAID 1 anyways thus the amount of data lose is minimal and next to none if you have a good UPS.2) Get a new raid controller that has 64mb+ of onboard cache and enable write caching and read ahead on the controller.3) Switch to RAID 0.
dmose
12 Posts
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Posted June 11th, 2007 17:00