DRIVE LOAD balance

[samar]

Hi,

Product NetBackup Enterprise Server, 7.1

System Solaris 10

library VTL: Fujitsu Eternus cs800

System solaris 10 , has two pathes to drive,

32  hcart2036            hcart2 TLD(0)  DRIVE=33
      /dev/rmt/55cbn                                                   UP
      /dev/rmt/77cbn                                                   UP

but it writes with only one path, iostat:

    r/s    w/s   kr/s   kw/s wait actv wsvc_t asvc_t  %w  %b device

    0.0  595.2    0.0 38087.5  0.0  0.2    0.0    0.3   0  19 rmt/77   

    0.0    0.0    0.0    0.0  0.0  0.0    0.0    0.0   0   0 rmt/55

How to make netbackup to write data through two path?

Thanks

[Mark_Solutions · Accepted solution]

NetBackup will not load balance to both paths like that.

It uses one path and can use the second path should the first fail but as far as i am aware multiple paths os for failover and not for load balancing

Hope this helps (sure someone from Symantec will correct me here if I am wrong)

[samar]

But before it wrote through both pathes .. After some time it stopped to write through both path.

[Marianne]

I agree with Mark.

See extract from this whitepaper:

http://eval.symantec.com/mktginfo/enterprise/white_papers/b-whitepaper_implementing_highly_available... 

Many SAN attached tape devices also offer two connections for redundancy and thus, appear to servers as two separate devices. Prior to the release of NetBackup 6.0, if both device paths were presented it was necessary to mark one path as unavailable to NetBackup to prevent device allocation conflicts. Multi-path awareness was introduced in NetBackup 6.0 and NetBackup now recognizes that both device paths map to the same physical device.
Multi-path selection is not dynamic; NetBackup selects the first available path it finds and always uses that path.
The second device path is only used if the first path is broken.

[Mark_Solutions]

"But before it wrote through both pathes .. After some time it stopped to write through both path"

How do you know that?

[samar]

as you see on graphic ..

[Marianne]

Maybe tape on FC0 and FC1 and disk on FC6 and FC7?

[Mark_Solutions]

From that graph all data is going in one direction (in)

So I guess we assume that is when it writes to tape.

How many tape drives do you have and one which ports are they mapped

So can we see a full map of your setup - or in orther words what in total is plugged into those 4 ports (just wondering if you have several drives with several paths and the four figures realte to different drives that share a port)

[samar]

VTL has 2 ports that listen clients, on which data comes from outside.

on picture it is FC0 and FC6

and other two ports are internal. You may ignore that.

Tape has 40 virtual drives.it shares all of his drives among other media servers.

FC0 goes to A switch FC6 goes to B switch.

and all media servers also connected to Aswitch and Bswitch.

so all media servers see 40 drives with 2 path like:

32  hcart2036            hcart2 TLD(0)  DRIVE=33
      /dev/rmt/55cbn                                                   UP
      /dev/rmt/77cbn                                                   UP

I have one server which is still writing through both paths. but others stopped to write like that.

[Marianne]

OK - VTL is not really tape. Disk is made to look like tape...

Maybe some disk-level multipathing that is/was doing load-balancing?

[samar]

Marianne thanks for reply,

OS doesnt see disks, of course on other end that are  disks, but OS doesnt know that, VTL emulates LTO.

VTL has 2 ports as i said above, it got data from outside via that 2 ports.

It writes exactly the same how it receives .. here i think point is on media servers.

i need to send data via both ports, not only one ..

[Mark_Solutions]

I still do not believe it is possible and without seeing you full SAN topology / zoning i cannot say why that data was passing across both ports - and if it was more importantly if it did so at the same time or worked on a round robin method, in which case still only one port gets used at a time