6.8.3 - cache drive build from 4 SSD in RAID 10 on HP gen9 D380 and P840 smart array controller - good idea ?

[salcio]

Hi, 

 

I've got a HP Gen9 D380 server with P840 smart array controller. 

 

At the beginning I've connected all the drives through on board ports so unraid can see them directly. I've set up a cache pool with 4SDD in btrfs RAID10 configuration. It worked ok (benchamark screenshots attached [SSD Metrics]). 

Then I though I should get better cache performance if I use hardware RAID10 though this P840 controller. And that what I've done - all 4 SSD are in RAID10 configuration on smart array. In unraid drive is formatted with BTRFS and set as cache drive. But the performance did not improve (decreased actually - screenshots attached []). 

 

Benchmarks were run from the VM with img file hosted on cache drive. 

 

 

So few questions: 

 

1. Is having a cache drive done through P840 a good idea ? (Pros cons) ? 

2. Is BTRFS a good choice for cache in this configuration - maybe XFS would be more performant ? 

3. In the banchmarks I'm not sure about the Acc. time - should that be something in range of 0.030 - 0.100 ? 

 

[BRiT]

I would possibly wait until or at least check out the unraid 6.9 Series and see if the way you want to allocate your "Cache Pools" changes.

[salcio]

With the current setup (4SSD through P840 RAID controller) there is only one Drive visible to unRaid. So no "Cache Pools" from unraid point of view. 

 

Are there any changes in 6.9 that affect cache. 

[BRiT]

Yes. There are changes in 6.9 that affect cache. That's why I said you should check out unraid 6.9 series and see if the way you want to allocate your "cache pools" changes.

 

 

You can have at least 30 different "drive pools", each with atleast 30+ drives. Somethere in there is the number 35, but I cant remember if it's drive pools or drives per pool. Needless to say. It's a Metric Ton of them.

 

So you could segregate your writes and optimize your performance in different ways.

 

So you may want a single SSD for docker/appdata and things that don't require more than a single SSD performance.

Then you would use the other SSDs for VMs.

 

 

 

[salcio]

That's sound awesome. It will defiantly help to split the caches per use case. 

 

Do you have any thought about the current setup ? 

Like why do i see drop in performance (small but still) between software (btrfs) RAID10 and hardware (P840) RAID 10?