Smart Array 6i - duplex drive configuration

[Casey Black_1]

What is the recommended configuration when using the duplex option on the DL380 G4. We have 6 drives and had planned to have 2 drives in a RAID 1 and the other 4 in a RAID 5.

Would we want to have the RAID 1 on one channel and the RAID 5 on a separate? Or would it be better to mix the RAID 5 between the two channels.

Thanks!

[Girma Kassa_2]

Hi Casey,

If you want the two raids on separate channel what you have described above is correct. However, make sure the SCSI back plain set to the embedded duplex SCSI configuration. This will give you SCSI id 0, 1 to channel 1 and Scsi Id 2, 3, 4, 5 as channel 2.

I hope this answer your question.

Cheers

Girma

[Casey Black_1]

Hi Girma,

Thanks for your response. My question is more around what is the "best" setup utilizing the dual channel capability. Split the RAID 5 onto two channels or keep it all on one.

Thanks again.

[Casey Black_1]

One other question that has come up... Is dual channel meant to offer redundency in any way. I can't see how it would, although I am getting mixed messages on this.

[Ruslan]

There is only one right configuration possible when using duplex scheme. First channel for RAID1, second - RAID5. Making array on 2 channels d't improve the perfomance, because there is overhead of data transfer between 2 buses

[GLL]

DON'T split a RAID anything between channels. If you do, you'll get a red LED on the front indicating an internal error, an SCSI #2 amber LED lit internally, and a Windows SCSI bus error (event 24683, CPQCISSE) indicating that its performance has been downgraded.
I found this out the hard way after my backplane failed and I let the HP tech replace it. He told me it was a firmware issue and left.

We were running simplex (all 6 drives on one channel) versus duplex--2+4. It was squwaking because in our setup, it was 0+1-2+3-5. O was OS, 1-2 were mirrored and 3-5 were RAID5. Drives 1 & 2 of the mirror were straddling the channels and it didn't like that.

[Oleg Koroz · Accepted solution]

None of the RED LED should be ON when Configuration done Properly or proper device connected, G4 support more configuration options opposite G2 or G3, where Customers sometimes incorrectly Configured and get RED LED..
Follow User Guide properly for: Hot-Plug SCSI Hard Drive Cabling
http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00292624/c00292624.pdf

Fault Tolerant (Redundancy) will support either configuration where proper RAID Selected and not depend from channels, as long it Connected to Hardware RAID controller.

Duplex configuration used for additional performance Improvement and Split of data flow between SCSI buses (channels), however split between channels, it doesn't mean, split between Physical bus on the System board, there will be only one assigned for Controller, no matter what you do with Duplex or simplex, you Controller will stay in U320 boundaries. Duplex give you chance for each dedicated Array (A, B) have own SCSI BUS with members as: Array Controller, Hard Drives and Cache Accelerator. Cache Accelerator keep reserved portion of Memory for array Controller and share rest for each channel, more chances to get Errors like: parity, Spin Up time, Bus faults when more confusion or different Array on the Same channel. Telling to cache accelerator that: Array A on the Channel B and Array B on the Channel A - eliminate portion of possible errors, and gave you additional chance to troubleshoot Problem in the Future by number of errors for each SCSI bus.
Additional Performance that you might looking from Duplex can be reached by using BBWC and more beneficiary to use additional Array Controller SA6400 for Channel A (RAID 5 or 4 HDD), where different HW Bus will be used from System Board.

However there is no bottom-line with performance for your needs, you might never see difference with either configuration and it really depend how busy your server with data flow, read / write operation, data access. You can try to make Simplex do some performance check, after divide to Duplex, all HDD automatically redetect (Roaming) them and run Performance once again. Spliting RAID 5 between different portions of SCSI backplane is less recommended.

[Casey Black_1]

Thanks for all your replies. They do seem contrary to what I read elsewhere i.e. other s recommend balancing the physical drives across SCSI channels. I might pose the question: What do you do when the number of disks in your RAID 5 exceeds the number of devices a single SCSI bus can support?

[Oleg Koroz]

RAID 5 - allocates parity data across multiple drives and allows simultaneous write operations. It is recommended for up to 14 hard drives per channel.

Generally design from low end to high-end newer servers; support for internal use, takes from 2 to maximum 6 drives per cage connected to one channel (ML530 & ML570 G1,G2 take two cages / except ML570 G3 it take 8 + 2 HDD's). So when time to use 14 drives or more, you talking about External Storage Enclosures, MSA, SAN, EVA ... etc.
Once again, before you heat needs to use 14 drives, options always to upgrade internal drives with bigger size (example 146GB swap to 300GB). Or you might use NAS Server.
http://h20000.www2.hp.com/bizsupport/TechSupport/Product.jsp?lang=en&cc=us&prodTypeId=12169&prodCatId=82653

http://h18006.www1.hp.com/products/servers/proliantstorage/arraycontrollers/index.html

http://h18004.www1.hp.com/products/servers/proliantstorage/arraycontrollers/documentation.html

[Casey Black_1]

Thanks KOV. My point was more that there is nothing invalid about splitting a RAID 5 between SCSI channels.

I spoke with HP support yesterday and they too indicated that this was the most common setup (mirror on one channel and RAID5 on the second). They did however say that splitting the RAID 5 was a valid configuration and that it should theoretically provide a performance improvement (as drive usage on the mirror piggybacked on the second channel would be minimal).

I ended up erring on the side of caution and using the common configuration.

Thanks again.