codyhosterman
3 Silver

Re: Query on LUN presentation to ESX clusters

I am not really sure how other OSes identify them, but my understanding is that most are more tolerant when it comes to LUN IDs. LUN 0 can be an issue for some though. If you have specific OS in mind I would try posting in those communities on ECN (Everything Microsoft etc.).

Highlighted
mattcowger1
2 Iron

Re: Query on LUN presentation to ESX clusters

Most modern systems (Linux DM, Windows 2008+, modern DMP, PowerPath) use the device WWN or NAA id to identify a device, and so LUN ID generally doesn't matter.  Now, that means you need to pay attention to which devices you are putting filesystems on, for example.

Example:  Using device mapper on linux, a given LUN can be accessed via:

/dev/sdX, Y and Z (the various individual paths, not multipathed and not failover safe)

/dev/mapper/dm-XXX (a multipathed device, but one that could be a different device if you add LUNs with lower LUN IDs, because they are enumerated in order

/dev/mapper/by-id/YYYYYYYYYY (a multipathed device that ALWAYS corresponds to the same device, regardless of LUN ID.  If the device changes LUN ID's, no change to this block device.  If LUNs are added or remove, no change.  This is a safest option.

Now, most applications that use raw disks or have modern filesystems can handle a LUN ID change anyways, but its still best to be aware.

Vsphere 5.5 never requires LUN ID's to be the same.

Gary_Grubb
1 Nickel

Re: Query on LUN presentation to ESX clusters

Thanks for the reply Cody. I will collect a list of OSs & multipathing software & validate them. Thenak for your help.

Nice work on the blog - I am following it closely.

0 Kudos
Gary_Grubb
1 Nickel

Re: Query on LUN presentation to ESX clusters

Thank you Matt. This helps.

0 Kudos