EVA4000 is not seeing availble space

[DallyAck]

I have an EVA 4000 with 20 146gb FCSCSI drives in a disk group called "FAST". I had used all but 500gb of the available space. I then added 6 450gb FCSCSI drives (2.7TB RAW) and added them to the "FAST" disk group. I was expecting to see approximately an additional 1.8TB of free space but my EVA shows only another 175GB! The disk group shows level pending for about 24 hours now but has not started. Where's my remaining 1.6TB or so?

[Malcolm Watts · Accepted solution]

Do you have an Unlimited License To Use code or have you purchased "x" number of 1 GB LTU licenses, as you might have gone over you allowed LTU quota.

[Víctor Cespón]

When you mix different sized disk on a disk group, the calculations on the available space are not straightforward, and you must wait until leveling finishes, because leveling redistibutes the data on the disks.

It has been explained on this forum recently, the EVA groups the disks on RSS and to avoid having a RSS with a lot more data (and therefore I/Os) than the others, it usually puts only one big disk per RSS.

This has an impact on the useable space, meaning that you cannot just think that you'll be able to use all the space on the big disk.

If you have a disk group with many small disks, adding a few big ones is not a good way to increase space.

In your case, the disk failure protection went from reserving 2*146 to 2*450 GB, so you lose 600 GB. Then, depending on how many vdisks in vRAID 5 you have, you'll only be able to use a fraction of the 450 GB disks.

Wait until leveling finishes and check numbers again.

[DallyAck]

Thank you. I just realized that I only added 6 450's They are the only 450's in that group. Do I have to add a minimum of 8 disks of the same size or is that 8 of the same type? ie. fata vs scsi

[Víctor Cespón]

You can only add FC disks to that disk group. FATA disks must be on it's own disk group.

The recommendation about adding disks in multiple of 8 is because the EVA forms RSS of 8 disks whenever possible, so if you add 8 more they will likely form a new RSS and do not modify the existing ones. Less data movement that way.

But that rule does not apply if the disks are different sizes. Performance takes priority here and the disks are scattered among several RSS, with the result that not all space on the 450 GB disks can be used.

So if you have a disk group with different sizes, you can not calculate available = total - used.

If you're curious about your current configuration, edit and run attached SSSU Script with SSSU.EXE "File SSSUscan.txt" > result.txt and attach it here.

[DallyAck]

I see... I'll wait until the drives level then confirm how much space is available.