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Craigondrums
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Performance degraded I/O on RAIDS

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My current configuration is: 

Dell PowerEdge R510 with PERC H700 RAID controller. I have 2 x 300Gb 15k disks and 6 x 600Gb 15k disks.

The 2 x 300Gb disks are on RAID1 for the OS

The 6 x 600Gb disks are on RAID10 for the DATA

If I add 4 x 600GB 15k disks on RAID10 would I see a performance drop in I/O on the other RAIDs? 

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pcmeiners
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RE: Performance degraded I/O on RAIDS

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So your adding a third raid...

The raid subsystem will be mostly affected by how much all the combined raids arrays are utilized, and how much bandwidth of the system bus is utilized, CPU/memory speed. If your server raids are hammered, it will affect I/O overhead. if moderately/mildly utilized, where the bandwidth of the raid adapter/ system bus are not totally utilized, and the raid cache is not overloaded, with occasional spike in usage, you would be hard pressed to notice any performance drop, if there is any drop at all.

If you go tweakers.net , (in Dutch, but you can get around without the language), they have benchmarks for all types of raids, and with multiple disk counts. From a few raid 10 setups I looked at it does not look like your proposed addition would saturate the system, I saw a few benchmarks with 12 drives which had performance gains over 8 and 10 drive arrays. Even though the benchmarks are for single array systems, you can judge how a multi array system will behave, aside from the fact benchmarks are placing a high load on the adapter/system.

There is no other site I have found with the degrees of raid benchmarks

http://tweakers.net/benchdb/suite/13

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Moderator
Moderator

RE: Performance degraded I/O on RAIDS

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Craigondrums,

Since it is a nested array (RAID 10), you will have to :

1. Create a new array with the new drives or:

2. Backup your data, add the discs and recreate your RAID 10.

Nested arrays (10,50,60) you cannot reconfigure. RAID 0, 1, and 5 you can reconfigure.

Each time you add drives to any array adds to the overhead, so I/O is going to be reduced, but not in a significant way. 

Regards,

Geoff P
Dell | Social Outreach Services - Enterprise


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pcmeiners
4 Tellurium

RE: Performance degraded I/O on RAIDS

Jump to solution

So your adding a third raid...

The raid subsystem will be mostly affected by how much all the combined raids arrays are utilized, and how much bandwidth of the system bus is utilized, CPU/memory speed. If your server raids are hammered, it will affect I/O overhead. if moderately/mildly utilized, where the bandwidth of the raid adapter/ system bus are not totally utilized, and the raid cache is not overloaded, with occasional spike in usage, you would be hard pressed to notice any performance drop, if there is any drop at all.

If you go tweakers.net , (in Dutch, but you can get around without the language), they have benchmarks for all types of raids, and with multiple disk counts. From a few raid 10 setups I looked at it does not look like your proposed addition would saturate the system, I saw a few benchmarks with 12 drives which had performance gains over 8 and 10 drive arrays. Even though the benchmarks are for single array systems, you can judge how a multi array system will behave, aside from the fact benchmarks are placing a high load on the adapter/system.

There is no other site I have found with the degrees of raid benchmarks

http://tweakers.net/benchdb/suite/13

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Craigondrums
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RE: Performance degraded I/O on RAIDS

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Great advice thanks all for you comments.

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