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# Understanding Drive's  Bus Number/TargetID/LUN

Posted on 2011-09-22
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right click on any drive->properties->Hardware Table->Click on Name of Drive and then see below drive properties

On a physical machine with SAN, I see

Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 0
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 1
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 2
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 3
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 4
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 5
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 6
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 7
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 8
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 9
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 10
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 11
Location: Bus Number 1, TargetID 0, LUN 0

vs

On a VM I see

Location: Bus Number 0, TargetID 0, LUN 0
Location: Bus Number 0, TargetID 1, LUN 0
Location: Bus Number 0, TargetID 2, LUN 0

Does that mean in the physical machines, there are 12+1 LUNs? There 2 Bus numbers what is the significanse of it?
on the VM, does that mean there are all in the dedault LUN of the datastore?
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Question by:25112
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LVL 121

Expert Comment

ID: 36580922
For the moment lets ignore physical and virtual machines, and look at some terms

Bus Number
This is the Storage Bus Number

TargetID
This is the method by which individual devices are identified on the Storage Bus. Often called a SCSI ID, each disk or chassis location has an ID.

LUN
A LUN is a Logical Unit Number. It can be used to refer to an entire physical disk, or a subset of a larger physical disk or disk volume. The physical disk or disk volume could be an entire single disk drive, a partition (subset) of a single disk drive, or disk volume from a RAID controller comprising multiple disk drives aggregated together for larger capacity and redundancy. LUNs represent a logical abstraction or, if you prefer, virtualization layer between the physical disk device/volume and the applications.

On your phsyical machine, you would have 13 disks presented to the OS, on Bus 0, SCSI 6, LUN - 0 - 11, and Bus 1, SCSI ID 0, LUN 0
On your virtual machinbe, you would have 3 disks presented to the OS, on SCSI ID 0, 1, 2

it's has nothing to do with datastores. Only the Physcial Server HOSTING the VM, has datastores.
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Author Comment

ID: 36581495
>>It can be used to refer to an entire physical disk, or a subset of a larger physical disk or disk volume. The physical disk or disk volume could be an entire single disk drive, a partition (subset) of a single disk drive, or disk volume from a RAID controller comprising multiple disk drives aggregated together for larger capacity and redundancy.

so many options there.. so just by looking at disk management it is not possible to tell what exactly or how small/big the LUN is, right?you need more tool as you said..
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>On your phsyical machine, you would have 13 disks presented to the OS, on Bus 0, SCSI 6, LUN - 0 - 11, and Bus 1, SCSI ID 0, LUN 0

2 bus- 2 devices- lot of LUNs is that typical of SAN
1 bus-3devices-1LUN - means like 3 exit doors on a bus? (one box availing itself 3 times)-more room for bottleneck?

-----------------------------
datastore- i understood from the other post that it is the basically the array or arrays of disk, and the supply for disk. I understand it for a VM machine, that its host holds the datastore.. what about in a purely physical server.. how do you define its datastore.

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Expert Comment

ID: 36581882
The LUN is equal to the disk partition or disk, so LUN 12 = a Disk Partition or Disk.

It is typical of a SAN, but could also be local attached Scsi Disk.

Yes, But The BUS is designed to commincate with multiple devices.

A physical server just has disks. There is not datastore on a phsyical disk.

Datastores are sepecifc to VMware hosts, where a bunch of disks or single disk is formatted with VMFS (VMware Filing System), this is a datastore, where Virtual Machines are stored.

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Author Comment

ID: 36582112
OK-
with the VM,
"
Location: Bus Number 0, TargetID 0, LUN 0
Location: Bus Number 0, TargetID 1, LUN 0
Location: Bus Number 0, TargetID 2, LUN 0
"
does it confirm that all 3 drives are part of the same LUN?

(perhaps other VM have drives part of this LUN, too, but which we do not know from the above) there may be more LUNs in the datastore or the LUN is the only one for datastore for the Hosting machine.. right?
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Expert Comment

ID: 36582129
No, Because each has a Seperate TagertID, SCSI Id.

Each is Unique.

do not consure host storage resources with virtual machines guests.

Until you have access to the host, you will never know, how Host Storage is configured.
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Accepted Solution

Andrew Hancock (VMware vExpert / EE MVE^2) earned 500 total points
ID: 36582159
It's possible that VMs, may or may not share the same datastore on the hosts, the hosts may have multiple datastores, connected to SANs or Local Storage.

There is NO WAY to tell, unless you have access to the HOST server, hosting rhe VMs.
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Author Comment

ID: 36582208
>>No, Because each has a Seperate TagertID, SCSI Id.

OK; I take that for the VM environment. thanks..

What about physical? does the same reasoning apply:  Each is not Unique?

Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 0
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 1
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 2
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 3
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 4
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 5
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 6
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 7
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 8
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 9
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 10
Port(2,2,2,2,3,3,3,3) Location: Bus Number 0, TargetID 6, LUN 11
Location: Bus Number 1, TargetID 0, LUN 0
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Expert Comment

ID: 36582261
No, because here the SCSI ID is the Same, it's 6, LUN is variable, so SCSI Address can contacted

0:6:0, 0:6:1 these could be disks, or Disk Units on a SAN/DAS, or storage which is presented to the server. (direct attached storage chassis)
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Author Comment

ID: 36594202
thanks as always..
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