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Max Number of disk in an Array - MSA1500 w/ MSA30

 
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Ningpa
Occasional Contributor

Max Number of disk in an Array - MSA1500 w/ MSA30

Is there a maximum number of disk you can have in RAID5 Array with the MSA30? One of our engineers was setting up an array and selected more than 14 disks. He got a warning notification that said this was against HP's best practices. Has anyone come across that? Does anyone know what HP's best practices for the MSA1500 cs w/ MSA30 disk enclosures are? And also, where do I find those best practices?

Thanks
By their fruit they shall be known...
4 REPLIES 4
James Muell
Valued Contributor

Re: Max Number of disk in an Array - MSA1500 w/ MSA30

The last time i checked, HP's recommendation for arrays was using 7 disk sets or higher. They had no published performance documents. The MSA30 enclosure has 2 busses slots 0-7 and 8-14. Start you arrays with 0 and 8. Spanning disk enclosures will affect performance. Example: If you have to set up a...14 drive array say, you would be best to use 2 enclosures w/ disks in encl-1 0-7 and encl-2 0-7. Thats about as much optimization as you can get out of the MSA1500/msa30 combo. I don't know if using the 6.86 fw and going active - active on the same lun would work any better. Haven't tested that yet. Good luck jm
Ningpa
Occasional Contributor

Re: Max Number of disk in an Array - MSA1500 w/ MSA30

Thanks for the reply. I have found the documents that state this. These are not best practices documents but installation guide. The rationale from HP is that, not having more than 14 drives in RAID5 array reduces the chances or probability of logical disk failure. I think this is one of those things that make you go "mmmmm". Unless someone cares to elaborate. Also I don't know if this apllies to RAID ADG arrays as well.

The document in question can be located (on page 16 point 4):

http://h20000.www2.hp.com/bc/docs/support/SupportManual/c00709035/c00709035.pdf

Francois
By their fruit they shall be known...
Uwe Zessin
Honored Contributor
Solution

Re: Max Number of disk in an Array - MSA1500 w/ MSA30

> The rationale from HP is that, not having more than 14 drives in RAID5 array reduces the chances or probability of logical disk failure. I think this is one of those things that make you go "mmmmm". Unless someone cares to elaborate.
>

There was an interesting session during today's SNW (Storage Networking World) in Frankfurt/Main, Germany. It was presented by a member from one of IBM's research labs.

Even with today's high quality storage, there is still a chance for what they called a "strip kill" - that is a non-recoverable block read error during a rebuild operation.

Not entirely surprising as there is a high load on the disks, because all data need to be read for recovery.

> Also I don't know if this apllies to RAID ADG arrays as well.

ADG (RAID-6, RAID-5DP) can cope with two disk errors - e.g. one total failure plus a "strip kill".

If I remember, Compaq/HP suggests to switch from RAID-5 to ADG if you intend to create disk drive arrays with more than 14 disk drives.
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Ningpa
Occasional Contributor

Re: Max Number of disk in an Array - MSA1500 w/ MSA30

Thanks for the reply! I will get the engineer to create the array with RAID ADG and see wether we get the same warning message.

Ningpa
By their fruit they shall be known...