Extremely slow on board raid 5?

[qstat]

I am newbie in this forum as well as raid 5. I just bought a DIY workstation with Intel I7-920/Asus P6T Deluxe/4 Gb Memory/Leadtek Quadro FX1700. The operational system is Windows XP SP3. I have five seagate 500 Gb (7200.11 I believe) SATA hard drives which are assembled with the on board supported raid 5. However, the speed of my raid 5 array is extremely slow, especially for the writing, which is at least 3 times slower than the hard drive of my laptop that I bought 3 years ago. I do not have a hard drive speed test software at hand, but I know the speed of my raid 5 is simply unacceptable. Therefore, I have several question below and hope to get answers from you experts in this forum:

(1) Is it normal to get such slow raid 5 performance?

(2) Is the slow raid 5 array related to the on board soft raid? If it is, how much improvement with hard raid 5 card can I expect?

(3) If a real hard raid 5 card is needed, could you recommend one with good performance/price ratio, as well as compatible with Asus P6T Deluxe MO?

(4) I am currently thinking about adding a SAS hard drive (P6T Deluxe supports it) to install the OS. Is it a good idea to have a non-raid SAS hard drive for the OS, along with a raid 5 array as backup/storage?

Thanks very much in advance.

Best, qstat

 

[Gatorbait]

Hi Qstat,

(1) Is it normal to get such slow raid 5 performance?
A) For a software RAID 5 solution you can get some performance issues. Especially if you don't have a dedicated CPU core for the RAID function.

(2) Is the slow raid 5 array related to the on board soft raid? If it is, how much improvement with hard raid 5 card can I expect?
A) Depending on how your Software raid is set up there will be a significant increase with hardware raid (not a cheap controller chip using a software RAID stack).
Here is the Reason: Software Raid used the same memory as the rest of your applications (and same processor core if not set properly). If the OS is running off of the RAID drive, then it further compounds the problem since that is normally where your virtually memory is located.

(3) If a real hard raid 5 card is needed, could you recommend one with good performance/price ratio, as well as compatible with Asus P6T Deluxe MO?
A) LSI is the leader in SAS RAID HBA to the Major OEMs. This means they will have good OS coverage, FW support, and Applications. I would suggest an PCI-Express version SAS 3.0Gbs version with memory on-board. Cost will be the issue... you may want to check out prices around the web for the best deal.
http://www.lsi.com/storage_home/products_home/internal_raid/megaraid_sas/value_line/index.html

(4) I am currently thinking about adding a SAS hard drive (P6T Deluxe supports it) to install the OS. Is it a good idea to have a non-raid SAS hard drive for the OS, along with a raid 5 array as backup/storage?
A) The simple answer is yes, but SATA300 in a stand alone drive attachment would give you more density/cost. Note: SAS hard drives are Expensive compared to SATA300 drives. SAS Drives lend themselves well to the RAID application. SATA300 protocol actually does have some better features than the original SATA drives for the RAID application.

Also, Drives use power and your PS will need to be significant.

Good Luck,
Gatorbait

 

[Gatorbait]

Also make sure you get the battery back up or force the card into write-back mode, this will increase performance.

 

[qstat]

Dear Gatorbait,

Thanks very much for your illustrative answers. Here is a little bit update after struggling with this piece of monster.

(1) I called asus custom service and was told that p6t deluxe does not support raid 5 that is larger than 2 Tb. Since I had five 500 Gb SATA II hard drives, I reduced it to four and raid 5 seems okay now. Considering the large seagate 1.5 Tb hard drive has been released, it is ridiculous that a larger than 2 Tb raid 5 can not be supported. Is it related to the NTFS system? Since p6t deluxe does not provide Linux driver for raid 5, I have to stick with Window XP 32-bit system. Maybe I should try Window XP 64-bit or vista or windows server 2003/2008, but I do not have license for either of them.

(2) I asked asus custom service which raid card is a good one working with p6t deluxe, but was told that its on-board raid 5 is the best choice. They simply do not recommend any pci card.

(3) I bought a 146 Gb SAS drive and tried to install window system on that SAS drive and leave the four 500 Gb raid 5 as backup. However, there is no way to install the system on the SAS drive. I called asus custom again and was told that my SAS drive can only be used as slave, because the raid 5 disk has to be my primary disk. I asked asus custom that if they have any plan to update firmware to support primary SAS + slave raid 5, but got no answer. I have no idea the technical difficulty for that setup. Anyway, there is not way for me to keep an expensive 146 Gb SAS drive as slave just to backup files! So I returned the SAS drive (sorry to my dealer).

Now I plan to use my extra 500 Gb SATA II hard drive to install the system and use the raid 5 disk (four 500 Gb hard drive) as backup. I will update later on this.

 

[qstat]

P.S. my PS is a silverstone 850 W one, which should be powerful enough. However, I do not know how to get the battery back up for on-board raid. Is there any way to do it?

Thanks, qstat

 

[Gatorbait]

Hi qstat,

There is no way to get battery backup for the on board RAID. This is a software raid style and therefore will use the main system memory for its XOR operations. It will be a write-through mode, where the OS will have to wait until the data is actually on the drive. Just buy a USP for your system and your good.