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RAID 5 or 6 for large partition?

Posted on 2011-03-02
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I'm rebuilding an array and am debating on RAID 5 or RAID 6.  Here's the requirements:
This server is very heavy on Writes, but not many Reads (it's a video recording server for our security cameras).  The application requires a single volume and can't write to multiple logical drives.  The drive will be full within 30 days and will then use a FIFO rotation scheme.  The total capacity has to be in the 2.5TB range.  I have (8) 450G drives to work with in an HP MSA60 chassis connected to a DL380 G4 running Windows 2003 R2.

Because my volume is over 2T, I'm using a GPT partition table vs MBR, but that shouldn't really matter in this scenario.

I could go with a single RAID 6 config with 2 hot spares, that will give me about 2.5T (6*450- 5%).

Or I could go with 2 RAID 5 arrays then span them in the OS to give me 2.5T (3*450 - 5% * 2).

What I'm really concerned about is the rebuild time if loose a drive.  At 4G per hour, it will take almost 30 days to rebuild parity - probably more because of the sheer volume of data that is replaced every day.  Is it better to have 2 spares in RAID 6, or smaller parity rebuild by using 2 RAID 5?  I've never been a fan of spanning partitions, how does that play into this equation?

Other recommendations?

Tim
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Question by:hundet
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by:BITCooler
ID: 35018046

Consider RAID 50 = Good Balance of Space utilizationi, Redundancy, and Write Performance.

I recently setup an HP Proliant DL380 G7 server 88GB DDR3 RAM with the following RAID config:
RAID 50 based on:
8 x 300GB 10,000 SAS drives
HP P410i Controller 1GB cache

Cache on your controller will make a huge difference.  Add as much as you can afford.

For the moment, I'm running a Citrix Xenserver 5.6 FP1 with Windows SBS 2008 installed as a Virtual Machine.
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by:Xav720
ID: 35018103
user raid 50 for performance but if is not a performance issue use  raid 5
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by:BITCooler
BITCooler earned 250 total points
ID: 35018203
I should point out, that I paid extra for the HP Smart Array Advanced Pack (HP Part Number 516471-B21) to unlock other features of the P410i controller.  This may have given me the RAID 50 choice.

A good source for making RAID knowledge is http://www.acnc.com/04_01_05.html

If you consider RAID 50 it's worth while reading this article from TechRepublic:
http://www.techrepublic.com/blog/datacenter/raid-50-offers-a-balance-of-performance-storage-capacity-and-data-integrity/2822

RAID 3 is suppose to be good for video streaming.

RAID 10 will give you better performance, but you will take a hit on available storage capacity.
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kevinhsieh earned 250 total points
ID: 35018271
Spanning in the OS isn't a good idea. Better to do RAID 50 at the controller level. RAID 6 will give the same capacity as RAID 50 and I think is preferable because you are less vulnerable in case of drive failure. Your video recording system may generate a lot of throughput, but the IOPS should be low which makes plays to the strength of RAID 6. I use RAID 6 with 8 2TB drives in my backup server and throughput is very good.

I am not familiar with the HP line, but my understanding is that RAID performance sucks unless your controller has battery backed cache. If you haven't already bought your drives I would look for 7.2K RPM nearline SAS drives which are perfect for your application. 10K SAS is overkill for this.
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by:andyalder
ID: 35035934
Can you afford RAID 10? Rebuild time is hours rather than days. Plus for video recording you could use 2TB midline SAS rather than enterprise SAS since it's sequential write so not much disk head movement.
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by:andyalder
ID: 35035952
Sorry kevinhsieh, you already said use 7.2K disks for video.
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Author Closing Comment

by:hundet
ID: 35059145
Went with RAID 6 - already had all the hardware, and it seems to be performing better than the original RAID 5 that we tried.

Thanks for all the comments.
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