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CharlieBeBop

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Battery Backed up Cache Equivilent with ZFS RaidZ2?

Is there anyway to get the performance benefits of battery backed up cache if you are not using hardware raid?  It was recommended we should use raidz2 to get the most benefit out of ZFS as a SAN for disk failure alerting and management.
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Brian Utterback
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I am not sure what you are asking. Are you saying you want to use BBUC with raidz2 and can't, or instead of raidz2?
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CharlieBeBop

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If you use a hardware raid controller, you have no knowledge in most cases when a drive fails.   I believe one of the main benefits of using Sun's ZFS Software raid is to be able to tell when a drive fails as it has intricate knowledge of the drive and it obviously has support for it (when hardware raid there is no uniform way of reporting this information).  

I was also told I should be able to see the same type of performance from software ZFS raid on a dedicated storage box as I would see using hardware raid controllers.   But battery backed up cache is a significant performance gain if you do not saturate the memory.   So I am wondering if there is a way to get that sort of performance using ZFS software raid considering you are not using hardware enabled raid.

I want to build a StoreVault type of clone using ZFS, so I am trying to find the best controller to use to get  maximum performance but also the best reliability.   I was looking at 3Ware 9560SE controllers in a Intel SSR212MC2 box but they do not seem to be supported under solaris and I was told if i am using ZFS for NFS/iSCSI SAN I would be better to use software ZFS for manageability but I should still see the same performance or better of hardware raid considering the memory/cpu is dedicated to storage.

I am also considering just using hardware raid and throwing VMWare right on the box and not using hot failover but have a standby chassis just to move the drives over in case of a failure, but I am likely to want to be able to use active fail over.
So, you are saying that the BBUC is a function of the raid controller, and since you will not be using the raid controller, you lose the BBUC?

Of course, BBUC is only useful for write performance. ZFS has generally very good write performance over most workloads, because it turns random write patterns into sequential write patterns. However, the point behind BBUC is increase the latency for data to hit persistent, reliable storage. There is nothing in ZFS that can do anything about the fact that the hard disk controllers must wait until the bits hit the disk to have the same semantics as when the bits hit the cache. I presume that the hard disk controllers do not have BBUC. But BBUC only decreases the latency of the writes, it does nothing to increase the data throughput, so for heavy usage BBUC is not a really ideal anyway.
BBUC is generally a function of the controller.  

As I understand it, even heavy usage benefits from BBUC providing two things, one you do not saturate the cache within the write period, two the transactions are not long sequential (high throughput) applications.

I am basically looking at the best option for using a Intel SSR212MC2 with Solaris 10 to build storage server.  I was planning on using an Intel raid controller for the BBUC and the fact it plugs right into the backplane.   I also can't find any controllers that support plugging into a backplane like Intel's SSR212MC2 that do not support raid (if I wanted to use ZFS to handle raid).
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Brian Utterback
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I will give it a try, I have been having loads of problems getting it to install in VMWare ESX and Workstation to do some testing so I will need to give it a shot on physical hardware.  I had problems doing it on bare metal DL140 G3 as well.  Couldn't find the CD to finish the install.