Legacy Device Files versus Persistent Device Files

[shikhar_1]

Hi,

Can anyone pls let me know whats the basic difference between Legacy Device Files versus Persistent Device Files? On which OS ver onward we are using persistent device file?

How to configure LVM using persistent device files?

[P Arumugavel]

hi,

Below is the recent thread posted for same query.

http://forums11.itrc.hp.com/service/forums/questionanswer.do?threadId=1458670

Persistent DSF was introduced on 11i v3.

Attached documents would give you a good idea on persistent device files.

Rgds...

[Jayakrishnan G Naik]

Hi Shikhar,

As mentioned by Vel-UX persistent device file is a default feature of 11i V3 , But with appropriate patching 11i V2 can also can use persistent device file feature. The persistant device files is a part of the 11i V3 feature called Native Multipathing.

The diffeerence is that, persistant device file maps all the device paths to a lun, (multipaths) to a single device file, While in legacy dsf, each path to the lun have a legacy device file which needs to be managed individually . They were called PV links.


Thanks & Regards
Jayakrishnan G Naik

[Torsten.]

As already said, the main difference is this:
with legacy device files you have multiple device files for a multipath device, no load balancing, e.g.

/dev/dsk/c1t0d1
/dev/dsk/c2t0d1
/dev/dsk/c3t0d1
/dev/dsk/c4t0d1


with the "new" device files you have a single device file with load balancing, e.g.

/dev/disk/disk7

[madhuchakkaravarthy · Accepted solution]

hi

on vgcreate or vgextend if so u created with
persisent device files

for eg

ioscan -m dsf /dev/rdsk/cxtydz

vgcreate /dev/vg01 persistent decive file

load balancing will be done,if one pv goes down it gets link from another pv,but in legacy device file

u have to do manually.

vgcreate /dev/vg01 legacy device file and then u have to add other disk with

vgextend other legacy file .

regards

MC

[jijesh.pc]

Hi ,
If you use command
#ioscan -m dsf

you will get the details of peristent device file names and legacy device files.

persistent device file using the world wide unique number of luns instead of the bus,target ,lun details of legacy device naming.
legacy device files will be in the form
/dev/dsk/cxdxtx block device file
persistent device file will be in the form
/dev/disk/diskn

[Ismail Azad]

Hi,

Just for your info.. A persistent device file is independent of the underlying controller. The device file "persists" accross reboots irrespective of what HBA the disk is connected to on the local server which is one of the biggest advantages of it being associated with the virtualized hardware address. If I change the topology , disks referenced via legacy DSFs change. This is the biggest difference. Legacy DSFs will be deprecated in a future release.

Regards
Ismail Azad