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I don't quite understand the significance of differences between the various Dell RAID controllers for my scenario, it would be great if you guys could help me choosing the right one. I don't want to burn money by buying something for no reason, but at the same time ensure that I'm getting what I need.

For my Dell R710 2U server with 6x 146 GB 15K RPM drives, I have the choice between the following controllers:

  • SAS 6/iR Integrated, x6 Chassis [automatically included]
  • PERC H200 Integrated RAID Controller [adds $199]
  • PERC 6/i SAS RAID Controller, 2x4 Connectors, Internal, PCIe, 256MB Cache [adds $299]
  • PERC H700 Integrated RAID Controller, 512 MB Cache [adds $499]
  • PERC H700 Integrated RAID Controller, 512 MB NV Cache [adds $699]
  • PERC H700 Integrated RAID Controller, 1 GB NV Cache [adds $799]

In case it matters, the server is going to run Windows Server 2008 R2, SQL Server 2008 R2, and IIS, and basically host various websites with varying degrees of complexity and SQL activity.

I want to run 3 RAID-1 arrays (2 discs each), with the OS/TempDB etc. on the first array, SQL data on the second array, and SQL log on the third array.

Really appreciate your help. Thanks!

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I'd ask dell pre-sales support. They know their hardware better than anyone. – Tom O'Connor Dec 18 '10 at 9:08
up vote 5 down vote accepted

For Dell, "256MB Cache" means 256MB of battery-backed cache on the RAID card. This is the cache used by the card for I/O operations. It caches writes in this storage to re-order them for more efficient usage of your disk. The battery is there in case of power loss, the battery supplies voltage to the cache-RAM. I believe it lasts up to 2 days.

"512MB NV Cache" means non-volatile. I don't know exactly how Dell does it, but I strongly suspect it has a normal RAM-based cache. A super-capacitor on the card has enough juice to commit the cache to flash-memory in case of sudden power loss. This will survive a power-outage for a lot longer than a battery-backed cache.

1GB NV Cache just has more cache.

The amount of data you're slinging around isn't that large to multiple internal connectors is not that important.

If you trust your power environment very well, a battery-backed cache will save you some money versus the non-volatile cache option.

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Which option would you recommend for my scenario for best performance while not spending unnecessarily? I don't think we'll have a power outage (DC has a 100% track record) so I guess we don't need the non-volatile cache versions. – AX1 Dec 18 '10 at 1:07
@AX1 NV cache is a better technology, but unneeded here. The 512MB Battery-backed controller should fit your needs very well. – sysadmin1138 Dec 18 '10 at 1:14
So the H700 for $499 is your recommendation? Thanks for your help. – AX1 Dec 18 '10 at 1:15
PSUs in machines blow. The NV option is always useful if you value your data even with redundant PSUs and a UPS. – JamesRyan Dec 18 '10 at 2:43
The server has indeed a redundant PSU, and i believe the H700 without NV cache still has a battery backed cache right? – AX1 Dec 18 '10 at 18:43

igiven your reqs, I'd go for the 699 option just for the non volatile cache

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Could you explain why please? Trying to understand the reasoning. – AX1 Dec 18 '10 at 0:49
because the nv cache prevents the databases from becoming corrupt/lose data on a long term power outage, all the writes will survive that and be written to disk as soon as the power is back on. – KutscheraIT Dec 18 '10 at 8:24

Based on 3 RAID 1 arrays I'd stick to the basic 6/iR or the 6/i with cache. The RAID 1 array is going to be the bottleneck although some cache may help a little. For web sites using slowly changing data sources then caching in IIS will give you the best performance. When using SQL you'll want to disable write-back cache regardless of the controller to ensure writes get to disk.

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We've had some servers with 6/iR's perform very poorly in certain situations (e.g., write-heavy DBs). The 6/i is a 3Gbps device, and the H200 is essentially a 6Gbps equivalent (you don't state if your drives are 3 or 6 Gbps). I'd recommend an H200 at the very least for those reasons, and if you're worried about IO performance and stability (as @sysadmin1138 mentioned earlier), spend the money for one of the H700s. – ktower Dec 18 '10 at 2:03
can you actually show me an SAS drive that can go fast enough to use 6Gbps? Also I doubt any performance blip that you saw was caused by the card. RAID1 is about as simple as it gets, the drives are the bottleneck. – JamesRyan Dec 18 '10 at 2:50

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