Best practice: Cascading 5 MSA70-Shelfs to P411/P800

[TimWebster]

Hi,

We want to cascade 5 MSA70-shelfs to one DL380G6 with full 146 15K spindles. What would you suggest if we plan to use P411 or P800.

a) Will there be more performance to connect 2 shelfs to one Port of a P411/P800 and one to the second sas-port of the same controller, to have 1 dedicated whole controller for one shelf due performance thoughts? We supposed to have the max. performance by using 3 Controllers. Or what would you do?

b) is there a max i/o throughput difference between the p411 and the p800?

Kind regards
Tim

[Johan Guldmyr · Accepted solution]

See http://h18000.www1.hp.com/products/servers/proliantstorage/arraycontrollers/index.html

for a comparision.

P411 have less cache which is very important. Especially if you'll be running RAID5 or 6.
P411 however have 6GB SAS/3G SATA while the p800 have 3G/1.5G

Both cards are PCIe 8x.

DL380 G6 can have 5 cards connected. And to get the PCIe slots you need to get the PCIe riser board options. "HP DL380 G6 3 Slot PCI-E Riser Kit "

a/ if you have the possibility, can you get 5 cards? Presumably with only 3 cards, you will have to have one MSA alone on one card. Not enough ports available.

[TimWebster]

Thanks for the quick and detailed response.

Now a question about parts of your answer:

"P411 have less cache which is very important. Especially if you'll be running RAID5 or 6.
P411 however have 6GB SAS/3G SATA while the p800 have 3G/1.5G"
-Yes, On the first point let me say that I will have only RAID5-sets in the 5 Shelfs.
In considering this condition, the adapter is then wrong?
-The second tells me, that the adapter (p411) seem to be anyhow faster with the SAS-connection. Now which adapter is better bis 5 shelfs and up to 50 x 146GB SAS 15K?
Will the P800 drive with 50 disks in the saturation?

The comparision btw, is a great site, thank you! The hint with the riser is perfect!

Now for the last point:
"if you have the possibility, can you get 5 cards? Presumably with only 3 cards, you will have to have one MSA alone on one card. Not enough ports available."
-So you would use also 5 cards? Is it really a performance benefit? Would the performance (max I/O) be degraded/ divided trough two shelfs on one P411/P800?(One Shelf per dedicated SAS external Port)

Does it work to have one MSA on a whole card or why did you ask?

Again, many thanks to you!

[Johan Guldmyr]

http://h18006.www1.hp.com/storage/disk_storage/msa_diskarrays/drive_enclosures/msa70/specs.html

The MSA70 only does 3GB SAS anyway, so the 6GB SAS won't be used if you have the P411.

Also from the quickspecs of the MSA70
http://h18000.www1.hp.com/products/quickspecs/12652_div/12652_div.html

"Supports HP 3G SAS Dual-port disk drives, (36 GB, 72 GB, 146 GB & 300 GB capacities)"
"NOTE: 6G SAS drives will only function as 3G drives in a MSA70"

Yes the RAID5 benefits a lot of the p800 controllers.
As far as I can tell now, the p800 controller is the way to go if you want to run this setup.

I've been trying to find some documentation about how fast the drives are so we could calculate how many it takes to saturate the 3GB link.

Another question you might want to get answered is if the 3GB is per external SAS port or totally per Controller Card.

I have not been able to find that now, maybe somebody else can help you with that.

(gotta get back to work now :)

[TimWebster]

Thanks again,

i´ve not been aware of the 3GB/s limit till you told me that.
Great answer!

Kind regards
Tim

[TTr]

Did you already buy the MSA70s? If not, consider the D2700, they are replacing the MSAs and support 6G SAS drives

http://h18000.www1.hp.com/products/quickspecs/13404_div/13404_div.html

You also have to realize that the two external connectore of the P411 (and the P800) each have a 4 SAS port bandwidth. This means that only 4 disks can be read by the P411 at a time. The MSA and the D2700 have SAS expanders built in to connect all the 25 disk drives to the 4 ports of their external connector. This is very similar to a LAN switch.

The P411 can have 512MB cache as well and it is newer than the P800. The cache on the P411 is 40-bit or 72-bit wide at 800MHz as opposed to 72-bit wide at 533MHz on the P800

The P800 also supports dual domain connectivity. You can connect both P800 external connectors to the same MSA or D2700 and double the bandwidth (however at 3G drive speeds). There is no mention of dual domain support for the P411.

[TimWebster]

Hi
thanks for the hint with the d2700 shelfs, i never heard from them before.

One Question to this part of your answer

"You also have to realize that the two external connectore of the P411 (and the P800) each have a 4 SAS port bandwidth. This means that only 4 disks can be read by the P411 at a time. The MSA and the D2700 have SAS expanders built in to connect all the 25 disk drives to the 4 ports of their external connector. This is very similar to a LAN switch. "
-How do i have to understand the part with 4 disks at the same time. Was this only a hint? Or do i have to use an other kind of controller to use the capability for to be able to read/write more than 4 disks at the same time?

I now wonder if we have to completely change the quote. Cause the 70s are not buyed yet. But what do i need "more" within the dl380 to use 5 d2700er except the p411?

Kind regards
Tim

[TTr]

The 4-disk access is a physical limitation of the connection. It is a 4-port connection from the P411 to the MSA/D2700. Inside the MSA/D the 4 ports are switched out like a LAN switch to the 25 disks/ports.