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## different size disks and performance

Hi All,

I have a brand new EVA with mixed speed disks.

15,15,15,15,15,10,10 | 10,10,15,15,15,15,15

the disks in the middle are 10k as shown.
15k - 146GB
10k - 300GB

if i put the disks in a mixed disk group at what speed will the disks run ?
is there a way of telling the EVA to just use only the 10k disks and create a disk group ?

thanks,

Sajeev
6 REPLIES
Honored Contributor
Solution

## Re: different size disks and performance

Hey Sanjeev,

If you put them all in single diskgroup, individual disk will run at it's own speed, there will not be any aggregated speed of the whole diskgroup. It's equal to the scenario that you have some of the busier disks in diskgroup which will eventually impact your overall performance because of the fact that data is written across all the disks.

With 14disks you don't have choice but to go for a single diskgroup (requirement for a diskgroup is minimum 8 disks). But if you have more disks then there are 2 ways to do it.

- Create a single diskgroup with minimum 8 disks and then selectively click on 10k RPM disks (or 15k RPM disks) then add them to Diskgroup one by one. At last check if any of the initial 8 disks is of different PRM, ungroup it. Then create another diskgroup with remaining disks.

- Create a single diskgroup with all the disks, and then selectively ungroup either 10k or 15k RPM disks one-by-one. At last create the diskgroup with all the ungrouped disks.

Hope that helps.

## Re: different size disks and performance

Hi I did not mean just 14 disks, i meant that as an example.
lets take this as an example:

15,15,15,15,15,10,10 | 10,10,15,15,15,15,15
15,15,15,15,15,10,10 | 10,10,15,15,15,15,15
15,15,15,15,15,10,10 | 10,10,15,15,15,15,15
15,15,15,15,15,10,10 | 10,10,15,15,15,15,15
15,15,15,15,15,10,10 | 10,10,15,15,15,15,15
15,15,15,15,15,10,10 | 10,10,15,15,15,15,15

how can i groups just the 10k disks together in CV.

thanks

## Re: different size disks and performance

ok i understood from the answer above. thanks
Honored Contributor

## Re: different size disks and performance

Hi,

You should also consider disk placement, that is, to vertically align all the disks across all of the shelves in your configuration. Try to line up all the different sizes/speeds as well as much as you can but overall all of the shelves should have no less than one disks diference between them.

Mark...
if you have nothing useful to say, say nothing...
Honored Contributor

## Re: different size disks and performance

Hi,

Forgot to put in!
If you physically align the disks [as suggested above] and only put in ONE type of disk then you will not need to worry about ungrouping the disks - this can take a long time. Then add in the other disks to create your next disk group.
Remember to add in all your disks into a disk group in one go as this will also save time when the EVA is levelling - however this may well take several hours as well.

Mark...
if you have nothing useful to say, say nothing...
Honored Contributor

## Re: different size disks and performance

Let reiterate.
The drives rotational speed is completely transparent to the disk controller/RAID controller. The increase rotational speed only effects how fast the individual drive can read/write the data received to the disk and be ready for the next. So if gruoped together, the faster rotating disk will complete 33% faster than the other. But again the controller is not aware of the disks rotational speed so there is no way for it to chosse groups for you, you would have to do that manually
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