Performance for RAID 5 SAS and HP 400i controller

Posted on 2013-05-24
Medium Priority
Last Modified: 2013-05-27
Please verify whehter my assumption is correct or not.

With HP 400i controller, the thoughput is 3Gb/s -> max througput is 375MB/s

Each SAS RAID-5 hdd will have transfer rate ~ 140MB/s, so probably 3 HDDs may overload the controller but the card normal support more than that.

So, what do I miss ?

Question by:AXISHK
  • 3
  • 2
LVL 47

Assisted Solution

David earned 800 total points
ID: 39196028
real world with 3HDDs you won't get anything close to 375MB.  Don't worry about it.   Why? Because writes involve reading data from 2 disks and writing to 1.  Then you have to consider filesystem overhead and extra writes any other write requires for the filesystem.

You'll also never sustain 140MB/sec anyway, that is how fast data is read from cache.

Author Comment

ID: 39198329
Any material concerned with this type of calculation ? For HP 400i controller (thoughput ~ 375MB/s), what's max disk that it can support ?

LVL 56

Expert Comment

by:Handy Holder
ID: 39198841
Max disks a P400 supports is 18 in a ML370 G5 but that's really down to the number of drive bays available in the server. QuickSpecs also claim 38 disks but there isn't any server that takes that disk arrangement.

I don't know where you get "max througput is 375MB/s", 8*3Gb SAS lanes = 2.4GB/s although the PCIe bus is only 2GB/s.

It really depends what I/O pattern you throw at it though, your 15K disk may be able to read sequentially at 140MB/s so if you had a disk based backup system then you you may be able to stream from a 3 disk RAID 5 at something like 250MB/s but if your operating system is running on those 3 disks then it's not going to be sequential access. Worst case is about 200 IOPS, which means you can read 200 512 byte sectors in 1 second = 100 KBPS per 15K disk. There are some ballpark raw IOPS figures in http://en.wikipedia.org/wiki/IOPS.
Making Bulk Changes to Active Directory

Watch this video to see how easy it is to make mass changes to Active Directory from an external text file without using complicated scripts.


Author Comment

ID: 39198872
3Gbps  = 3,000,000,000 bps -> 3,000,000 kbps -> 375,000 kB/s -> 375 MB/s

Do you mean there are 8 lanes in P400i with 3Gb/s for each lane ?


LVL 56

Accepted Solution

Handy Holder earned 1200 total points
ID: 39198936
Yes, there are 8 * 3Gb SAS lanes. In a simple 8 disk backplane configuration such as in a DL380 there is one lane per disk but the P400 also supports the SAS expander card that fans-out those 8 lanes into 24 lanes to allow 3 disk cages although the per-disk bandwidth is obviously less in that scenario.

Author Closing Comment

ID: 39198972

Featured Post

Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

For anyone that has accidentally used newSID with Server 2008 R2 (like I did) and hasn't been able to get the server running again because you were unlucky (as I was) and had no backups - I was able to get things working by doing a Registry Hive rec…
This article provides a convenient collection of links to Microsoft provided Security Patches for operating systems that have reached their End of Life support cycle. Included operating systems covered by this article are Windows XP,  Windows Server…
This tutorial will walk an individual through the steps necessary to enable the VMware\Hyper-V licensed feature of Backup Exec 2012. In addition, how to add a VMware server and configure a backup job. The first step is to acquire the necessary licen…
Despite its rising prevalence in the business world, "the cloud" is still misunderstood. Some companies still believe common misconceptions about lack of security in cloud solutions and many misuses of cloud storage options still occur every day. …

569 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question