bradje1
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Disk Speeds

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Hi,

I note the following:

NOTE: The default setting for Disk Cache Policy for virtual disks based on SATA drives is Enabled; and for virtual disks based on SAS drives is Disabled.

Why is the SAS cache disabled? I thought it would make the disk faster to Enable it.

Is there a comprehensive White Paper discussing the various RAID settings for the latest controllers?

Thx,

John Bradshaw

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RE: Disk Speeds

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Hello

I'm unaware of a white paper that explains the cache options. The options are explained in the OMSA storage manual, page 48. The second storage manual on the page is the correct link. I have already reported that the installation guide is mislabeled as the storage manual:

www.dell.com/support/home/product-support/product/dell-openmanage-server-administrator-9.0.1/manuals

Why is the SAS cache disabled? I thought it would make the disk faster to Enable it.

Yes, enabling the disk cache should increase performance, but it is not battery backed. If there is a sudden loss of power or a hardware failure in the RAID chain there is an increased chance of data loss/corruption if the disk cache is enabled.

I don't know the reason why we enable SATA cache by default, but I suspect it is likely due to complaints about performance on SATA drives. The performance difference is not usually as noticeable on SAS drives.

Thanks

Daniel Mysinger
Dell EMC, Enterprise Engineer

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Moderator
Moderator

RE: Disk Speeds

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Hello

I'm unaware of a white paper that explains the cache options. The options are explained in the OMSA storage manual, page 48. The second storage manual on the page is the correct link. I have already reported that the installation guide is mislabeled as the storage manual:

www.dell.com/support/home/product-support/product/dell-openmanage-server-administrator-9.0.1/manuals

Why is the SAS cache disabled? I thought it would make the disk faster to Enable it.

Yes, enabling the disk cache should increase performance, but it is not battery backed. If there is a sudden loss of power or a hardware failure in the RAID chain there is an increased chance of data loss/corruption if the disk cache is enabled.

I don't know the reason why we enable SATA cache by default, but I suspect it is likely due to complaints about performance on SATA drives. The performance difference is not usually as noticeable on SAS drives.

Thanks

Daniel Mysinger
Dell EMC, Enterprise Engineer

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bradje1
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RE: Disk Speeds

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Thx Daniel. Quite helpful as usual !!

JB

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