HPE Storage Users Group

Hello,

We currently have a two 3.5" cages each with 12 2TB disks. Is it possible for us to install 4TB disks in the same cages? Or is it required to stay with the same drive size?

Thanks,
Dan.

It is absolutely supported to mix drive size. You'll eventually end up with an uneven load, but since NL drives aren't really supposed to have much load on them at all that shouldn't be a concern (you do have a tier that's not NL, right?)

We do have a small amount of FC drives, but we are not using them much. This storage is mostly for file storage only. No virtual machines.

By uneven load you mean that because the drive is twice the size that there will be more load on the 4TB drives?

Dan

Correct, assuming average IOP density is constant over time (probably not a good assumption, but perhaps good enough) then you'll end up with twice as many IOPS per disk on the new spindles.

We have been forced down the path of installing different size disks in our mix.

Our T800 was originally bought with 50GB SSD drives and as they are no longer available are being replaced as they fail with 100GB drives. Our total free capacity increased as the 100GB drives are introduced
Currently it seems that the 100GB drives are holding the same amount of data (they are showing twice the free capacity than the 50GB drives).
From what we understand. If we were to fill the 50GB drives, the 100GB drives would then start using the remaining 50% of their capacity which in our case, would leave this data unbalanced (not across all SSD spindles.
I am assuming it would be the same for NL and FC

Thank you, this is exactly the info I needed. I think I will stick with the same size drives on these cages.

Dan.

Excuse my ignorance....

Reading through the forums a bit more, I came across some information about raid levels on cpg's using more than two cages.

Currently we have two cages with 12 2TB each, but if we wanted to expand the system I should be buying 12 more 2TB disks with another cage so that I have three cages available to do cage HA?

If I have a third cage I can do 2+1 for cage HA?

Still a bit confused about mirroring. I currently have a cpg that is set to raid 1 with availability set to cage. From what I understand I am able to lose an entire cage with no data loss. Does this also mean that I cannot lose two drives (one from each cage) at the same time?

Thanks,
Dan.

You need 4 cages to do cage availability with NL (RAID6 6+2)

--
DD
--
DD
--
DD
--
PP
--

where D= Data and P=Parity

Technically with 3.1.2 you can force NL to use Raid 5, but I believe they will be removing it (at least from the GUI) in a future release and I would strongly recommend against it as there's a non-insignificant chance it will lead to data loss through either unrecoverable read errors or through a rebuild taking too long on the big slow spindles.

*edit*
just noticed you mentioned RAID1/0, with RAID1/0 you can do cage availability with any even number of cages. If you have cage availability you will never have the two mirror copies of a block in the same cage so you can lose an cage without data loss, but if you lose the right two drives you will lose data, also if you lose a drive and the other copy is on a disk with an unrecoverable read error you will lose either that bit of data or the vvol (not sure on implementation details here).