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Drive shelf problems with large RAID 5 configuration

steno1122 asked
Medium Priority
Last Modified: 2010-04-03
The company that I work for has a Dell 2850 connected to a Dell PowerVault drive shelf.  The shelf is used as a large file share for the company.  Lately users have been complaining that file access is extremely slow.  The drive shelf was configured before I started here and the person who set it up configured the shelf as one giant RAID 5 partition.  The shelf has 15 drives and the RAID 5 set is over 1600 GB!  Management has asked me to fix the file access latency problem but I don't know if that’s possible in the current configuration.  I think the problem is due to the inefficient RAID 5 setup.  I know there are limitations to RAID 5 sets and I’ve read that having very large RAID 5 configurations is not recommended.  The shelf should have been configured in a few smaller RAID 5 sets instead of one giant one in my opinion.  Does this make sense?  Does anyone agree with me that the large RAID 5 set could be the problem?  What is a good size for a RAID 5 set for a drive shelf?  I’m looking for ammo so I can recommend to management that the shelf be reconfigured.  

Also, is there a good way to measure throughput on a SCSI controller?  The server is connected to the shelf via a PERC 3/Di controller.  I want to make sure the controller isn’t being over utilized but I’m not sure how to test it.  The server is running Windows 2003.  Are there any utilities from Microsoft, Dell or third party companies that will give me throughput info on the SCSI controller?

Thanks for the help!
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You can use Windows Performance Monitor tools to take a look at things like disk queues and so on.

But - back to basics first.

How full is the disc?
How many concurrent users?
Does the performance problem occur when you read a file, or when you write a file?
How badly fragmented is the file system? You can download a trial version of Diskeeper from http://www.diskeeper.com/defrag.asp?pass=822317868 and run an analysis and defrag.
Can you also go into Dell OpenManage Disk Manager and check the properties on the PERC 3/Di and check the status of the cache and the cache backup battery?

Just a little bit of homework :-)
hi, there

The connection from the Server to the storage should be a Perc3/dc, the perc3/di is only for the onboard raid controller. So if you do not have a perc3/dc and you are then connected through the perc3/dc or a perc4/dc then this is a non supported issue regarding the Dell.

Regarding the hard drive I will recommend no more than 7 drives in a Raid 5 here is where the top performance lies.
So as you said the ammo you will need is that the parity that is going to be written to the disk is best on 7 disks.


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