extending volume group on differrent controller

[Dave Chamberlin]

I currently have a 17G disk on the built-in fast-wide SCSI controller. I would like to
add a 4G disk to this vg so I can mirror 4G. The only controller I have to add it on
to is a 28696A wide SCSI. Will this work? ( I want to be able to reduce the 17G
lvol to 13G and then create a 4G lvol with one mirror.) The man page for vgextend
mentions that HP-IB devices can't be used in the same vg as other devices, but
what about HP-PB? Is FW SCSI incompatable with W SCSI for this purpose?

[Alan Riggs]

To the best of my knowledge you can add a drive on an HP-PB controller into a vg with FW SCSI without problem. Obviously, write performance on the mirrored volume will be affected.

[Venu_2]

Hi,

I gree with alan. There naturally will be a performance degradation of the mirrored volume as both controllers operate at different transfer rate.

If it is acceptable you can go ahead with mirroring

regards

venu

[Stefan Stechemesser · Accepted solution]

There is no difference for LVM to communicate via PCI, PB or HSC/GSC cards and F/W diff. is on all three bussystems at the same speed !!! But: If you have more than one card installed on one PB-bus, the performance may drop:
F/W D SCSI Card:always 20 MBytes/sec max.
PB-Bus speed: 32 MBytes/sec
HSC Bus speed: 160 MBytes/Sec

[Manju Kampli]

HP-IB disks can not co-exist with FWD and FDDI, where as FWD and WSCSI disks you are using should be able fall under same Volume group. Since there is a performance difference between WSCSI and FWD SCSI, it may slower the read/writes on FWD SCSI disks.