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Could someone explain to me how the Disk Cache Policy works, specifically on the LSI MegaRAID cards? I've recently installed a 9260-8i since I plan to setup a RAID5 with 8x2TB drives (3x2TB drives in array now). I've left the Disk Cache Policy set to the default of "Unchanged", the other options are as follows:

Disk cache policy: Select a cache setting for this drive:
Enable: Enable the disk cache.
Disable: Disable the disk cache.
Unchanged: (the default) Leave the current disk cache policy
unchanged.

How does the Disk Cache Policy work? If I enable it do the 64MB caches on the drives compliment the 512MB memory on the RAID card? Or does enabling it only make use of the cache on the drives and ignores the RAID card?

If you're wondering, this is just a storage array using Seagate ST2000DL003 drives. Most it needs to do is stream 1080p video files over the network to various computers/consoles.
 

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Iconoclast
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Chances are that the cache on the drives is invisible to the RAID card and cannot be disabled/enabled anywhere but the drive's own firmware.

I suspect the option you are looking at refers to the card's cache or a buffer in system memory.
 

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Hi guys,

That setting should enable or disable the cache on the disks themselves. You would usually want the on-disk cache disabled because it isn't battery backed like the cache on the RAID card & the card can't be sure when the drive reports back that a write has completed it might have only made it to the cache & not all the way to the disk platters.

It might not be that big a deal if the system is stable, on a UPS that can shut itself down and isn't doing a ton of IO, but if the writes get to far ahead & you have an outage you might get some corruption.

-Will
 

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set to enable depending upon the level of data integrity that you are looking for.
Speed will be faster with drive cache enabled.
 
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