Question

SAS Dual Port vs RPM

Asked by: thinktech07

I am configuring a new HP Proliant DL360 G5 Server and when it comes to hard drive performance I am questioning what is more important.  Does going with a Dual Port SAS hard drive at 10,000 RPM give better performance than a Single Port SAS hard drive at 15,000 RPM or vice versa.  I would love to get Dual Port SAS and 15,000 RPM but my budget won't allow for it.  Any suggestions?

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Asked On
2007-12-21 at 18:01:05ID23039433
Tags

sas

,

dual

,

single

,

vs

Topics

Storage Technology

,

Computer Servers

,

Computer Hard Drives

Participating Experts
3
Points
500
Comments
9

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Answers

 

by: warrenbucklesPosted on 2007-12-21 at 20:45:37ID: 20517746

Dual port seems to be pushed as a reliability enhancement rather than a speed enhancement, so my first-cut suggestion would be to go with the 15k drives - they will have higher sustained transfer rates due to the faster platters as well as less rotational latency when compared with 10k drives.

wb

 

by: andyalderPosted on 2007-12-22 at 03:38:27ID: 20518323

I agree. Although you may buy dual port disks and the backplane is dual ported it is unlikely that your OS supports dual RAID controllers in active/passive mode so you aren't going to gain any redundancy. The Pxx RAID controllers do not seem to have the capability to mirror write cache between them (although they may be able to do it through the PCIe bus) so even if there was OS support you would have to disable the write cache on the controllers for failover to work.

If you look at the MSA60 and 70 you'll see that they also have room for a second SAS host interface but it isn't currently supported. HP seem to be quite slow on this, IBM have had a dual-attached SAS shelf for 6 months but we're still waiting on HP .

 

by: thinktech07Posted on 2007-12-22 at 06:42:50ID: 20518673

I had read this in the following article which made me question if the Dual Porting gave better performance than the 15K RPM.

"Dual porting provides two separate data paths, allowing for higher levels of performance and eliminating single points of failure."
http://www.wwpi.com/index.php?option=com_content&task=view&id=853&Itemid=44

I had not questioned whether or not the Dual Port Drives were supported by the server because they came up as an option in the QuickSpec sheet for that server that HP provides. They also come up on this PDF from HP saying they are supported for the HP Proliant DL360 G5.
ftp://ftp.compaq.com/pub/products/servers/proliantstorage/drives-enclosures/SAS%202.5_Sep07.pdf

If it is supported I was under the impression that I would have twice that amount of data transfer per drive and I did not know how that compared with 15,000 RPM over the 10,000 RPM.

Can you show me where you saw that the P400i controller would not support the Dual Ports?  Thanks for all your help.

 

by: andyalderPosted on 2007-12-22 at 07:25:04ID: 20518781

>"Dual porting provides two seperate data paths".

Indeed it does; one goes to controller A and the other to controller B just like fibrechannel; thus if one controller fails the other controller can access the data on the disk instead. It is not dual-ported disks that are not supported at the moment but dual controllers. The dual-ported disks are supported but only through a single connection at the moment so the second port is unattached.

In future I dare say you will be able to put two P400s in a server both connected to the same disk backplane, I don't see that as much of an advantage though since the server's motherboard is a single point of failure. Dual-ported are more likely to be useful in a SAN-like environment with the disks connected to two servers for a simple 2 node cluster, that's why I mentioned the MSA70 since it's obviously designed for 2 node cluster support in the future.

As far as bandwidth is concerned a single disk does not benefit from being dual-connected since the bus is far faster than the disk. You can attach 100 disks to a single 4-lane channel on the P800; that's 25 disks per 3Gb channel and your DL360 has a whole 3Gb dedicated to each disk.

 

by: thinktech07Posted on 2007-12-22 at 07:32:33ID: 20518791

Thanks for your help andyalder.  It appears I will just go with the 15,000 RPM Single Port solution.  Happy Holidays!

 

by: andyalderPosted on 2007-12-22 at 07:48:54ID: 20518857

No probs. Can I suggest re-open and assign 50:50 split between me and Warren. He was certainly right and posted before me.

Merry Christmas! (I may not believe in God but I'm getting fed up with this new practice of hiding Christian traditions in fear of upsetting other faiths. I say Happy Diwali to my local shopkeeper just like he says Happy Christmas to me)

 

by: thinktech07Posted on 2007-12-22 at 08:09:21ID: 20518910

Actually I thought I gave you 300 and him 200 but now I see I have you the other 200 as well.  How do i reopen it to change the points?

 

by: andyalderPosted on 2007-12-22 at 08:28:03ID: 20518961

I don't know, they changed the site again!

The report abuse link seems to be the simplest way; not that it in any way implies abuse but it does post a Q in CS for you.

I tried it out:
www.experts-exchange.com/Community_Support/General/Q_23039901.html

 

by: Vee_ModPosted on 2007-12-22 at 11:14:28ID: 20519488

@Andy - thank you for doing that.
We've been fighting over the wording of that button.
Everyone thought it was going to be 'Report Problem', but TBTB changed it to abuse without telling us.
I will offer no further comment at this time. ;)

Reopened by Expert request.
V

20120131-EE-VQP-002

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