The LUNS and Seperate disks

[Simon M Appleby]

One last question in regards to the LUNs and external disks.

I have an AutoRaid unit and 5 other seperate disks, which I assuming are in a disk pack, and are sperate to the machine and AR.

Now the question is this.

Does anyone know of if the AR and the sperate disks be included into a LUN ? e.g 2 external disks and say using 1 or 2 diskd from the AR ?. Is this possible and how can this be done ?.

Thanks

:)

[Roger Baptiste]

Hi simon,

No. Lun is an Autoraid concept. The autoraid controller is the one which manages disks which are in its unit and presents them as a virtual disk called LUN.
So, you cannot include any disk outside of the Autoraid and in the Raid configuration for the purpose of including it in the LUN.

Again, remember that LUN is nothing but a disk from the System point of view.

If you have external disks, you will see it as a regular disk on your system.

If your motivation is to bunch a group of disks together, you can still use VGCREATE command at the system level and achieve it.
But, i would prefer disks of autoraid to be on a separate VG and other external disks on a different VG.

HTh
raj

[Simon M Appleby]

That sounds good now I understand the concept.

Have running the ioscan -fnkCdisk and getting all the info via that, of which I am trying to understand. How can you from this read which disk is attributed to which LUN ?.

Do you know much about "lssf" ?.

I am not sure of how to read this, because the sperate disks as mentioned above are showing up in this and are show them registared under LUN 0, is there something I missing in the interpution of this and given the info you gave about not mixing the AR and seperate disks, this seems somewhat to fly in the face of what is being said.

see below :-

IOSCAN

disk 6 0/52.6.0 disc3 CLAIMED DEVICE SEAGATE ST34371W
/dev/dsk/c4t6d0 /dev/rdsk/c4t6d0
LSSF


disc3 card instance 4 SCSI target 6 SCSI LUN 0 section 0 at address 0/52.6.0 /de
v/rdsk/c4t6d0

Any help in what does what in these reading would help.

Thanks

:)

[Marc Dijkstra]

'Ang on!

There are two devices on the bus with the same ID. 0/52.6.0. You have a 4GB disk and LUN0 of the 12H on the same bus at the same scsi addy?
c=controller
t=target
d=slice (lun)
/dev/rdsk/c4t6d0


Does a dmesg throw up SCSI resets? /var/adm/syslog/syslog.log errors?

MND

P.S: The PV /dev/dsk/c4t6d0 at the top is the hard drive. Even if this was chopped up at an LV level it would still be /dev/dsk/c4t6d0.

On the 12H (with it's SCSI id set to 5)one could create say 2 LUNS they would show up as
/dev/dsk/c4t6d0
/dev/dsk/c4t6d1

Effectively creating 2 PV's

[Marc Dijkstra]

hmm.... haven't had my morning coffee!

IF the 12H was at SCSI id 5 it would be

/dev/dsk/c4t5d0
/dev/dsk/c4t5d1

blooper....

MND

[Roger Baptiste · Accepted solution]

Hi,

Do not get misled by the term LUN. Every disk whether it is a standalone or as a part of RAID is shown as "LUN" in the lssf command.

Let me give an example:
For instance on my system, internal disk (which is just a plain standalone hard disk)
is a Seagate 18Gb disk as
shown below on diskinfo
#diskinfo /dev/rdsk/c2t2d0
SCSI describe of /dev/rdsk/c2t2d0:
vendor: SEAGATE
product id: ST318404LC
type: direct access
size: 17783240 Kbytes
bytes per sector: 512

When i do lssf (which list special file command) on the disk id , the output is:
tpc:/home/tester>lssf /dev/dsk/c2t2d0
sdisk card instance 2 SCSI target 2 SCSI LUN 0 section 0 at address 0/0/2/0.2.0 /dev/dsk/c2t2d0

As you can see it displays it as LUN 0 (which is nothing but it is the 0 logical unit number and since it is the only disk there won't be any more Lun numbers shown on the disk)

Now, i do the same commands on a EMC Lun (this is not exactly a physical disk, but a partition of disk. The system though sees it as a disk)

tpc:/home/tester>diskinfo /dev/rdsk/c46t1d5
SCSI describe of /dev/rdsk/c46t1d5:
vendor: EMC
product id: SYMMETRIX
type: direct access
size: 31426560 Kbytes
bytes per sector: 512

This is a 32Gb disk (lun)
I do lssf on it:
tpc:/home/tester>lssf /dev/rdsk/c46t1d5
sdisk card instance 46 SCSI target 1 SCSI LUN 5 section 0 at address 0/6/0/0.8.0.13.1.1.5 /dev/rdsk/c46t1d5

What do you see? It shows it as lun 5, which corresponds to
d5 -> 5.

In your case, you are seeing a seagate disk and running lssf on it which it shows as LUN0 (corresponding to d0)

To make it short, from VG point of view, Lun, disk are all the same. The term is used interchangeable.Also, for seeing free disks (or all disks on a system) use ioscan and diskinfo. That is where you get the useful info.

lssf is for seeing device file info.

HTH
raj

[Simon M Appleby]

Then reading is and hopefully correctly, every "d0, d1" e.g /dev/dsk/c1t1d0 and /dev/dsk/c1t1d1" are infact the LUNS - so "d0" will equate to LUN 0 and the "d1" will then equate to LUN 1 ?.

With your example you have given, what arethe difference between the "dsk" and in your case "rdsk", anything ot nothing ?.

I have noticed one other thing when reading a print from the HPArray "arraydsp" that the disks that reside within the AutoRaid are the ones that have an "alternate Link Path" and the others can be attached disks will reside outside the array, is this so ?. Then if that being the case these disks could be grouped or in a disk pack of sorts. Can LUNS be assigned to them to ?.

[Roger Baptiste]

<>

Yes, you are right. But that really does not matter in any way, because whether they are lun0 or 1 or 2, they are still disks to use.

<>

rdsk is the raw device file
dsk is the block device file.

A disk can be accessed either as a raw device or as a block device. Filesystems are accessed using the block device file dsk and raw volumes by raw device file rdsk. The difference, raw accesses the disk directly, whereas block accesses the disk through filesystem structrues. (sort of ).


>

I don;t use HP arrays, so am not sure about the command output. But, alternate link paths are paths which are another way to reach the disk.
So, a primary and alternate path both point to same disk, but through different cards.

>

I am not sure about the question. If you are referring to creating luns:
the way to do is:
Use the NAtive disk utility to create LUNS. (hp array would have its own set of commands.) All the luns you create are basically clever partitions of disks based on striping and protecting against failures.
Then, these luns are seen as disks at the system.

If the whole things seems confusing, take it piece by piece. Look at it first from a filesystem level, then go down to LV level, then to VG level, then to PV level, then to disk(LUN) level, then to the hardware .

HTH
raj