How do I know if I have PV Links

[Scott Hewes]

How can I determine if PV Links is available on a K260 server? I want to set up alternate paths to my EMC Symmetrix disk array. Currently I can only see one hardware path, and device file, for each disk in the array.

Thanks in advance...

[Patrick Wallek]

You will not see the PV links displayed if you do an ioscan. ioscan has no clue about pvlinks and will just show each disk separately.

PV links come into play when you do a 'vgdisplay -v vgname' on a VG. When it lists the disks that are a part of the VG at the end of the output, it will list whether or not there is more than one path to a particular disk.

[Wilfred Chau_1]

vgdisplay -v vgname

you will see something like this:

PV Name /dev/dsk/c11t15d7
PV Name /dev/dsk/c12t15d7 Alternate Link

[Jeff Schussele]

Hi Scott,

Do an
ioscan -fnC disk
and note all the /dev/dsk/cXtYdZ entries
If you notice a pattern of diff "c" entries with identical "t" & "d" entries, then do a
diskinfo /dev/rdsk/cXtYdZ
for both the diff c devices.
If you get the same info from both of them then the chances are good that you do have alt links.
Then try to vgextend the VG with the alt link.
Now any vgdisplay -v /dev/vg_name outputs will show the new link as an alternate link.
It's advised that you alternate the diff channels as primary/alternate - it's a kind of poor man's load balancing.

Of course, using the EMC symm* commands would be much easier.....

Rgds,
Jeff

[Michael Tully]

If you can only see on hardware path, where are you looking ? If you have a second path set up with cabling etc, the the second path should appear in the 'ioscan' output. Once you have established you can see a second path, you can add these logical disks to your existing volume groups with 'vgextend'. These logical disks will appear a second path. 'vgdisplay -v' will show you.

[Sridhar Bhaskarla · Accepted solution]

Hi,

Ask your EMC people to provide you with the utility "inq". It will give you an output containing the devices files as well the serial numbers. Using the serial numbers, you should be able to find the alternate paths.

Another way is to export and volume groups with map files and import them back with -s option. Once imported, if there are alternate links, system will add them automatically to the volume groups.

One interesting way is to find out the VGID of the disks and then add them to the volume groups. Here we are finding all the disks corresponding to one volume group and add them so that the alternate links are also added. To do it, run the following script.

for DISK in /dev/dsk/*
do
VGID=$(echo 0x2010?2X|adb $DISK|awk '{print $3}')
echo $VGID $DISK >> vgid.out
done

sort vgid.out > vgid.good

In vgid.good file you will find the VGIDs in the first column and the corresponding disks in the second column.

Take one reference disk from each volume group (strings /etc/lvmtab or vgdisplay -v vgxx) and find out the VG ID corresponding to that Volume group by using the adb command given above on that disk. Using that VGID, get all other disks having the same VGID from vgid.good file. Find out the disks that are not already part of this volume group and they are your alternate links. You can extend the vg using those device files.

Once it is done, doing a "vgdisplay -v " will give you alternate links.

-Sri

[Scott Hewes]

All of you replies are very helpful.

To answer Micheal Tullys' question, I am using ioscan which does not show me any other disks. There are 18 physical disks (LUNs) in the array, but ioscan only shows me 18 disks and not 36 as I guess I should see from what I understand about alternate paths.

I really like Sris' script to check the VGIDs of the currently configure VGs against disk that are not in any VG. Using this script though does not reveal any other "alternate" disks.

I do have two SCSI interfaces connected to the EMC and the EMC CE has divided the 18 disks across the two controllers where each controller has 9 disks.

[Jeff Schussele]

Hi Scott,

Well, it looks like they way EMC zoned those disks you won't be able to get alt links. They need to zone them such that all LUNs are seen to both HBAs.
This will most likely require *some* downtime as EMC will have to apply a new config to the array.

Rgds,
Jeff

[Marco Santerre]

Actually Jeff, I'm not a SAN expert but given the little bit of experience I have with EMC, downtime for new bins (reconfiguring LUNs on HBAs) is not necessarily required anymore. Depending which level of microcode you are at on the EMC array, it is possible to have a bin installed in the array without downtime. In this case, it is more than likely that this can be done without any impact to the array or the server.

[Scott Hewes]

Thanks for you help folks. It sounds like I'll need the EMC CE to come back out to re-configure the disk array. I hope that he can re-configure the array to support alternate paths without harming the current hardware paths that the K260 is using. Do you know if he can setup alternate paths without changing the current hardware paths?

[Marco Santerre]

Yes he can set up alternate paths and won't touch the current ones you have. All you'll need to do after he's done (which he will say will probably take up to 5 business days at least), is do an ioscan -fnC disk and a insf -e to see your new path (naturally you'll need to hook up your new HBA physically as well before you can do that