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kreisbote
Contributor
Contributor

All iSCSI targets must have different LUN IDs

I discovered a strange problem using iSCSI storage with ESX 3.

We have two storages (SAN/NAS box with Open-E DSS software on it) providing iSCSI targets.

The ESX servers access the targets by QLogic HBAs (QLA 4052C).

I could create and use the first target (at all) without any problems and it performs well. But if i create another target (even on another storage device) the esx-server could not distinguish between the targets because they both have LUN ID 0.

If i set the LUN ID to 1 on the other target, everything works fine.

By definition, each target can have multiple LUNs, starting with LUN 0. So i don't see the point why esx can't distinguish between the targets by name, but only by LUN ID.

Any hints ?

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5 Replies
oreeh
Immortal
Immortal

ESX requires different LUN IDs with (most) iSCSI targets.

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BUGCHK
Commander
Commander

So i don't see the point why esx can't distinguish between the targets

by name, but only by LUN ID.

In a multipath situation, several target ports present alternate paths of the disk on the same LUN address - the name does not matter. VMware ESX server requires additional information on the LUN - most likely an entry in the SCSI page 0x83 (a 'serial number'). Otherwise it became confused if you presented different[/b] disks from another[/b] storage array with other[/b] target IDs, but the same[/b] LUN addresses.

Not all targets seem to support this or it is a configurable option being turned off by default.

This is not new - I have seen similar problems in the Fibre Channel world on Tru64 Unix and a single storage array presenting 3 different disks via a single path. The vendor had to tweak the array to give the SCSI LUNs unique identities besides to LUN address.

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oreeh
Immortal
Immortal

or it is a configurable option being turned off by default

Most IET based implementations (using the old IET source) aren't configurable.

With the newer IET code you can configure the VPD 0x83 stuff - but as you said it is turned off by default.

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BUGCHK
Commander
Commander

Ah yes, I have been been lurking on the IET developer's mailing list for a short time and if I remember correctly, one of the challenges is how to provide a unique value in a consistent way.

Some Fibre Channel arrays use their front-end or back-end WWN and some instance-specific code for the remaining 64 bits.

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acr
Champion
Champion

EqualLogics present all their LUNS as Target 0, never have any issues..

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