Disk Enclosures
cancel
Showing results for 
Search instead for 
Did you mean: 

Command View EVA 5.0

afointWPI
Frequent Advisor

Command View EVA 5.0

Does anyone know why when you first initialize an EVA and create the default disk group, it asks you for Disk Drive Failure Protection of none, single, or double? If the Virtual Array's you create are using RAID5, why do you need this second layer of disk drive protection, you lose so much of your storage space by using this, and if it's not needed, i would rather leave the DDFP at none and just use RAID5 for my arrays...
7 REPLIES
Ian Vaughan
Honored Contributor

Re: Command View EVA 5.0

Howdy,
The Disk Drive protection level is there to reserve enough unallocated space to do rebuilds in case of disk failures. It is always worth having at least Single sparing (even if you are creating vraid5 disks) as then you can theoretically survive 2 failures in the same original RSS as long as the data has levelled off the bad disk before the 2nd failure occurs.

Without a single "Spare" you could fill your unallocated space up with snapclones & new disks etc - 2 disk failures in the same RSS would result in data loss in the vdisks in that Disk Group.

HTH
Ian
Hope that helps - please click "Thumbs up" for Kudos if it does
## ---------------------------------------------------------------------------##
Which is the only cheese that is made backwards?
Edam!
Tweets: @2techie4me
Frantisek Kysela
Valued Contributor

Re: Command View EVA 5.0

Hi,
it's the same as "hotspare disk" in another arrays. In EVA is this function realized as hotspare capacity across all disks in disk group.

Frantisek
If anything just cannot go wrong, it will anyway.
afointWPI
Frequent Advisor

Re: Command View EVA 5.0

Ok, so the DDFP is an extra layer of protection, however, we plan on always keeping at least 2 spare disks that are not in the default disk group, that way a disk failure would be short-lived, and setting the DDFP to none because it eats up almost 1 TB of space for this. Does anyone also know why you can not create a virtual array larger than 2 TB (2048 MB)???
Uwe Zessin
Honored Contributor

Re: Command View EVA 5.0

The so-called "protection level" is not another level of redundancy. It is only a space reservation - like Ian wrote: think of it as a spare disk, except that it is rotated by 90 degrees and distributed over all disk drives in the disk group.

> Does anyone also know why you can not create a virtual array larger than 2 TB (2048 MB)???

I think you meant: "virtual disk", not virtual array.
A limit in the SCSI protocol: 2^32 blocks * 512 bytes/block = 2 terabytes.
.
Mark Poeschl_2
Honored Contributor

Re: Command View EVA 5.0

By keeping two disks "spare" not in the default disk group you would require manual intervention to recover from a single drive failure (potentially). If you add those disks to the default disk group and set the sparing level to "single" your recovery is completely automatic and transparent.
Uwe Zessin
Honored Contributor

Re: Command View EVA 5.0

Right, and the other good thing is that you have two more disk assemblies for physical I/Os. Ungrouped disks will draw power, but not do any useful work.
.
afointWPI
Frequent Advisor

Re: Command View EVA 5.0

Thanks or all the help guys, I think I got it now. I setup one disk group using all the disks and set the protection level to double. This will essentially give us two spares ready to go. I then setup a virtual disk using RAID5.