Maximum drives in an HSG80 Spareset

[Stephen LeGrow_2]

What is the maximum number of drives that can be in an HSG80 spareset?

[Robert Atkinson]

My guess in no limitation outside of the maximum number of drives a HSG can handle, but why would you want more than say 10 - are you expecting a lot of failures?

Robert.

[Stephen LeGrow_2]

I am adding some larger drives to my SAN and I want to add some spares of the same size. I will end up with no more than 10-12 spares.

[Robert Atkinson]

I can't see that being a problem at all. If there were a limit, it would be a magic number like 255.

Robert.

[Wim Van den Wyngaert]

There are HSG80 limitations.

Maximum 128 visible LUNs/200 assignable unit numbers
Maximum 512 GB LUN capacity
Maximum 72 physical devices
Maximum 20 RAID-5 storagesets
Maximum 30 RAID-5 and RAID-1 storagesets
Maximum 45 RAID-5, RAID-1, and RAID-0 storagesets
Maximum 8 partitions of a storageset or individual disk
Maximum 6 members per mirrorset
Maximum 14 members per RAID-5 storageset
Maximum 24 members per Stripeset
Maximum 48 physical devices per striped mirrorset

It's not specified but it could be as low as 14. So test it.

Wim

[Stephen LeGrow_2]

So if I add six 146GB drives it and create a RAIDSET and a single LUN it will only recognize 512 GB? Or will it not let me create the LUN at all?

[Robert Atkinson]

The LUN in your case is the 146GB disk hung on to the end of the cable, so this doesn't break the 512GB limit.

You can add up to 24 members into a stripeset, up to the maximum size VMS can handle (2TB or 4TB seems to ring a bell).

Rob.

[Robert Atkinson]

Stephen, one more point.

As long as you've got a reasonable amount of resilliance in each unit (i.e. RAID, MIRROR) then you only need a couple of disks in each SAN spareset.

Ensure these are as large and as fast (15K RPM) as your largest disks, so they can take the place of any disk.

We've had our 2 HSG80 SANs for a number of years now, and apart from when we completely rebuilt it to add more disks, I've never seen more than the odd disk go bang.

Robert.

p.s. We've recently gone to EVA, so if you're looking to purchase any HSG hardware, I have 2 full SAN's for sale!

[Stephen LeGrow_2]

All of our LUNS are either RAID5 or Mirrored, thanks for the tip.


We will be moving to an EVA hopfully within the next year or so.

[Wim Van den Wyngaert]

We had the case where a disk of a raid said was lost and before the reconstruct of teh spare was done a 2nd disk of that set also broke down. Not in prod though.

Wim

[Uwe Zessin]

> Maximum 512 GB LUN capacity

1 TB in recent ACS versions.

> Maximum 72 physical devices

84 on an EMA-12000 with recent ACS versions.

--

> The LUN in your case is the 146GB disk hung on to the end of the cable, so this doesn't break the 512GB limit.

No, it is not the back-end disk drive. The limit is at the storage-set / unit level.

> You can add up to 24 members into a stripeset, up to the maximum size VMS can handle (2TB or 4TB seems to ring a bell).

The SCSI-2 protocol provides support for 2 TeraBytes (2^32 blocks a 512 bytes).

OpenVMS supports 1 TB volumes - looks like it cannot deal with unsigned integers ;-)

[Stephen LeGrow_2]

1 TB in recent ACS versions.

> Maximum 72 physical devices

84 on an EMA-12000 with recent ACS versions.

--

> The LUN in your case is the 146GB disk hung on to the end of the cable, so this doesn't break the 512GB limit.

No, it is not the back-end disk drive. The limit is at the storage-set / unit level.

> You can add up to 24 members into a stripeset, up to the maximum size VMS can handle (2TB or 4TB seems to ring a bell).

The SCSI-2 protocol provides support for 2 TeraBytes (2^32 blocks a 512 bytes).

OpenVMS supports 1 TB volumes - looks like it cannot deal with unsigned integers ;-)


We are at software version V88F4 for our HSG80 controllers so I should be able to create a LUN larger that 512GB correct?

Our SAN is not connected to a VMS system.

[Robert Atkinson]

Uwe - surely in this case a LUN is the equivilent of a PTL, rather than a unit?

Rob.