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Broken RAID5 performance

Posted on 2006-06-12
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Last Modified: 2010-04-03
I have a server and im wondering what happens if the Raid 5 image breaks..

Will the server still work and regenerate the data on the fly ? Will that be too slow? The server has a dual 3.4 ghz and 3 gb mem
and scsi drives. Hardware raid.

Please get back to me asap.

all the best
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Question by:daxa78
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5 Comments
 
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Expert Comment

by:Lee W, MVP
ID: 16883761
It's never a good idea to put something into a production environment without knowing what will happen if it fails and what YOU will do to recovery it.  So test now before it goes into production.
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Expert Comment

by:Lee W, MVP
ID: 16883768
That said, RAID 5s can loose ONE disk - if that happens, disk access will slow - not to a crawl, but it WILL be slower than if the RAID were in tact.  Depending on the hardware configuration and the features supported, the RAID MAY rebuild itself automatically - if you have a hot spare OR when you swap in a new drive - OR you may have to initiate the rebuild - exactly what you have to do, again, depends on what your hardware supports.
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Expert Comment

by:rindi
ID: 16883777
When one disk of a raid five array (not an image) fails, Performance shouldn't yet be compromissed too much. Once you replace the bad disk, depending on the raid controller and disks, you can do that without shutting down the server, but first make sure it is hot pluggable! Once the new disk has been connected, the array should be rebuilt automatically. This will reduce the performance noticeably. Depending on the controler, again that will be automatic, but with some older models you may have to do start the rebuild yourselve. If you set up the raid with a hot spare in the first place, the controller should automatically start rebuilding the array with that disk without you having to intervene. while the array is rebuilding it is better not to shutdown or reboot the server!
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Author Comment

by:daxa78
ID: 16883935
The name of the raid controller is

FSC RAID CTRL ONB. Key ITBBU 128 MB LSI and i do the modifications before the server boots
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Accepted Solution

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Todd_Bunch earned 500 total points
ID: 16888956
When using a Raid configuration the controller will write data to all drives in the Raid. If you have a single drive fail the raid will continue to work. This allows you time to get a replacement drive. The fall off when one drive has failed is not bad at all, most users do not notice at all.

In most cases the controller has infomation on it about the raid configuration, there is also a copy of that information stored on the RAID itself. In the case where the controller itself fails you simply install the new controller, (Same type) and it can recover the information from the drives.

One very important thing to remember is the RAID controller has batteries and they drain over time. If you have a raid that is working and the server is 3 years old or older then there is a good chance when you shut down the server the controller will not have saved that data any longer and the server will not start.

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