I have a R720xd with 1 CPU (4core E5-2609), 16GB ram, with an H310 and 12 x 2TB SAS drives in the front.  OS is Centos 6.

My write performance seems to be stuck around 500MB/s so I decided to experiment and observed the following.

I put all 12 drives in non RAID mode and then proceeded format them as ext4 and mount them all individually.  Then I created a script using dd to create a 20GB file on each drive, sleeping for 20 seconds between each start of dd in the background.  In a separate window I had iostat going with a 2 second interval.

What I observed, is that up to 4 drives it looked like I was limited by the drive bandwidth.  Iostat was showinf about 140MB/s writes to each drive up to 4 drives.  After that as each successive dd kicked in another drive the average per drive dropped.  With 5 drives avg 103MB/s, 6 drives avg ~83Mb/s, and so forth with the aggregate sum being somewhere between 500 and 550MB/s.  

Is this what I should expect?  Seems like the iowait and system time is pegged during this.  Would having an extra CPU help?  Or how about switching to a different driver controller (plain HBA?)?  OS tuning?

On the read side there is no degradation in performance from 1 to 12 drives it stays between 140 and 150MB/s for each drive (over 1.5GB/s aggregate !!)

Hello create123

I combined the two threads for you.

This is a known issue. There is currently no ETA on when or if this will be addressed with a future firmware update. If it is possible to correct the issue with a firmware update then I suspect it will be fixed in the future. The issue is only present when the H310 is in JBOD/non-RAID mode. The issue is not present in the H200, and it is noted that in a JBOD configuration an H200 performs better than an H310 because of this issue.

You might try putting the two SSD's in a RAID 0. I am not sure if the issue will affect RAID drives with JBOD in use, but it is noted that the issue is not present in RAID mode. Based on your testing it sounds like the controller is treating the drives like a SCSI bus rather than a point to point connection. It appears to be slowing down to the slowest member disk because it is waiting on confirmation commands from the HDD before performing another request, but that is just conjecture on my part.

Thanks

Thanks for the info.  Is there somewhere I can sign up for updates on this issue?

I'm actually going to partition the SSDs into separate RAID 1 and RAID 0 for ZFS ZIL and L2ARC once I can make sure it all performs well in a supported setup.  So I need to keep the SSDs in JBOD as I don't think the H310 supports that. Can I fit an H200 in my R720xd?  What parts would I need to plug the front backplane to an H200 (assuming it works) and the back SSDs to the existing H310?

thank you.

Can I fit an H200 in my R720xd?

The H200 is not a supported controller on the R720. The system is only designed to support functionality of a single integrated RAID controller(H310, H710, or H710P). The 2 add on slots in the rear are cabled off of the backplane. Those slots are in backplane extensions. I don't think it would work if you cabled one of our controllers directly to those slots.

Are you talking about slicing arrays on the SSDs, putting a RAID 0 across both of them on part of the available space and then a RAID 1 across them on the remaining space? I thought you weren't supposed to mirror the cache drives. I'm not very familiar with ZFS or caching with it via ARC, but I think you should be able to configure the two SSDs as single drive RAID 0's.

Thank you again for your helpful info.

Re H200: I was thinking of an H200 in one of the standard PCIe slots like this person did: en.community.dell.com/.../19882873.aspx

Anyhow, if I understand you correctly, the connection between the backplane and the 2 add on slots is not some standard SAS connection variant and therefore can not plug them into a SAS HBA using approriate cables.

So until the H310 is fixed (if possible), sounds like my best option (if I want JBOD) is to use a SAS HBA like the LSI 9211-8i in IT mode in one of the PCIe slots.  Is that card compatible with the backplane+add ons in the R720xd?

Regarding ZFS, yes I was referring to slicing the arrays on the SSDs.  The ZIL is a write cache (intent logs) and best practice is to use a mirrored SSDs for data integrity.  The L2ARC is a level 2 read cache and striping is usually the preferred setup for size and performance.

Anyhow, if I understand you correctly, the connection between the backplane and the 2 add on slots is not some standard SAS connection variant and therefore can not plug them into a SAS HBA using approriate cables.

Correct, it may be possible somehow, but they are not designed to be directly attached to a controller.

So until the H310 is fixed (if possible), sounds like my best option (if I want JBOD) is to use a SAS HBA like the LSI 9211-8i in IT mode in one of the PCIe slots.  Is that card compatible with the backplane+add ons in the R720xd?

The only controller's listed as compatible for the backplane are the H310, H710, and H710P. I'm not sure why you are restricted to JBOD mode, but you may consider single drive RAID 0's on any of the above controllers as an alternative.

Regarding ZFS, yes I was referring to slicing the arrays on the SSDs.  The ZIL is a write cache (intent logs) and best practice is to use a mirrored SSDs for data integrity.  The L2ARC is a level 2 read cache and striping is usually the preferred setup for size and performance.

Yes, the H310 supports up to 16 virtual disks per disk group, so you can have 16 RAID 0 or 1's across those two SSD's. If you did that you wouldn't be able to create arrays across any of the other drives though as the maximum virtual disk count is 16 as well.

Thanks

I got an update on the firmware. I was informed that the issue is not correctable with firmware, so this problem will not be resolved.

Yes, I apologize about the issue. If you would like to reach out to your account team about switching to an H710 I will explain the issue with them to see if we can do a swap and only pay the difference.

One other question...does this problem apply to the H310 adapter also or only the integrated one?

Thanks I'll do that.  

What kind of throughput should I expect with a RAID 10 (same as above) using that card.  My drives are 12 x 2TB SAS 7200rpm.

Hmm... don't like the sounds of that.

Anyhow I decided to check out the performance of the H310 with RAID 10 (6 spans of 2 PD per span) and dd maxes out at just under 400MB/s.  I was doing slightly better with JBOD and software RAID.  I am in the process of creating 3 different RAID 0 of 6, 4 and 2 drives to see how those perform.  So far can't say I'm happy about this setup.

Don't mean to be snarky, but those are the stated specs for the H310 too and look where it got me.  I originally selected it because it was the only one supporting pass-through.

Anyhow, I have requested a quote for the H710P.

those are the stated specs for the H310 too

Correct, there is a known issue with the H310 not being able to achieve rated specifications.

One other question...does this problem apply to the H310 adapter also or only the integrated one?

All versions of the H310 to my knowledge.

It will be able to easily max out what your drives are capable of. It has 8 ports that are capable of 6Gb/s for a total throughput of 48Gb/s(~6GB/s). If your account team has any questions for me then have them search the corporate directory for Daniel_My. I'm the only one that will show up.

http://www.dell.com/downloads/global/products/pvaul/en/dell-perc-h710-spec-sheet.pdf

Thanks

So I had a look inside finally and the rear backplane uses a standard SAS connector.  Do you know if it is possible to connect this to the SW raid SAS connector on the motherboard?  Is that connector active if an integrated RAID card is installed?  

This could mostly solve my problem of the performance degradation that my SSDs are suffering while being connected to main backplane.  If they are separate then I am ok with my HD raid maxing out at 400-500MB/s if this means the SSDs are not impacted.