on the hidden part of first four disks of first enclosure (is always SCSI/Fibre but never ATA). 5th disk is also used for some more data apart from OS boot image.


No, They could be part of "meta luns", they can also be the luns used for other array features like clones or snapshots.


Private LUNs are LUNs reserved to be used for caching purposes such as the Reserved LUN Pool and Cache Private LUNs - LUNs that the array needs for layered applications. private luns are also used for metaluns. when you combine more than a lun to form a big lun, the chunks used to combine become private.


refer primus solution emc1053 if you are very sure you can delete this


no, you cant move hidden data off first 5 disks. they would be labled on the array, unless someone removed it.

#On one of the RAID arrays with ATA drives, I notice 4 'private luns' of each 3GB each. Is this where the OS is located?

OS is not located on the Private Luns....As a matter of fact, nowadays OSes are pre-installed. As far as the 4X3GB private luns are concerned, I suspect them as MetaLuns or a part Snapview Clones i.e CPL's...

Thanks a lot!!

yur welcome!

* The OS is installed on the first 5 disks, do I see anything about this in Navisphere? (a special LUN? or just some disk space that I can't allocate to a LUN?)
no you cant see this in navisphere. you can only see a PSM lun that keeps trespassing between two SP. if you create a RG on first 5 drives and another on any drives of same size except first 5 drives, you can see that the first RAID group is smaller by few GBs. this is the hidden space on first drives.


no...this caching is done for layered drivers while you are using snapview or mirrorview features. if you destroy these luns, you will not be able to create snapshots or mirrored luns across two arrays. these luns do not cache sp read/write cache.
read write cache on array is utilised using memory chips that are on the storage processor.

Thanks for the answers! But as all good answers do, the create some new questions

* The OS is installed on the first 5 disks, do I see anything about this in Navisphere? (a special LUN? or just some disk space that I can't allocate to a LUN?)
* The Private Luns on my ATA drives are marked 'Reserved LUN Pool', any idea what they are used for? We have read and write cache enabled on one of the LUN's in that raid group. So my guess is, that if we destroy the RAID group, it doesn't mather that the private luns are gone too, since they are used for caching on a array that doesnt exist anymore. Correct?


Thanks again!!

So in order to safely destroy the RAID group on my ATA disks, I need to create 4 new LUN's (on my scsi disks, since all ATA disks are in this RG), add them through 'Configure reserved lun pool' and remove the other 4 (all of them have allocation: free)?