Replace failed disk in EVA

[deandyno]

I have a failed drive in my array, I have a spare drive that I can use to replace the failed one. The original drive is a 148GB 15k drive, the spare is a 300GB 10K drive.

After reviewing the HP StorageWorks EVA configuration best practices whitepaper I was left with the impression that keeping like sized/speed disks was recommended, but if you needed to mix them go ahead is that impression correct?

[IBaltay · Accepted solution]

Hi,
from the performance side, it is not a good idea to mix disk sizes in the DG, nor the 10k and 15k, but it is supported...

abstract from here:
http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&objectID=c01846577&jumpid=reg_R1002_USEN

Mixing disk capacities influences performance
Best practice for performance optimization: Purchase and create Disk Groups using equal capacity disks.
Best practice to optimize performance when disks of unequal capacity are present: Unless there is a specific plan to manage the differences in access density of the Disk Groups, it is preferable to combine disks with different capacities in the same Disk Group.

Disk performance selection influences array performance
For applications that perform large block sequential I/O, such as data warehousing and decision support, disk speed has little or no effect on the net performance of the EVA. An examination of the disk data sheets would confirm that the average, sustained, large-block transfer rates are similar for both 10K- and 15K-rpm disks of the same generation. As such, large capacity 10K-rpm disks make the most sense for large-block sequential workloads.
Best practice to optimize performance: 15K-rpm disks provide the highest performance.
Best practice to optimize price and performance: For the equivalent cost of using 15K-rpm disks, consider using more 10K-rpm disks.

[Greybeard]

simply put, you would be adding the capacity to your disk group, not directly replacing a disk since the EVA is all about available capacity not individual disks :) Be aware though that if all the other disks are 146 and you have a disk protection level set (single or double) you could LOSE available capacity by adding a 300 as the protection capacity is calculated using the largest disk size. So single uses 2x146 in a group of 146GB disks, add a 300GB and you use 2 x 300GB

[AWilliams_1]

Note too that the 300GB disks will actually have twice as much data on them as the 146GB disks. eg if the 146 disks currently have say 70GB of data on each disk and you replace one with a 300GB disk then that disk will end up with 140GB on it. This is what causes the performance problem with mixed capacity disk groups.
I think in your case that you would be ill advised to use the 300GB disk unless you plan on adding more 300GB disks to the group.

[deandyno]

Thanks to all for clarifying...

[deandyno]

Thanks