Ubuntu on IBM z Systems

Bug #1592990
Comment #13

Comment 13 for bug 1592990

Revision history for this message

Christian Ehrhardt  (paelzer) wrote on 2016-06-20:

#13

Just looked a bit with jfh who prepped a similar setup - thanks.
jfh found some issues when recreating like: "fdasd: ioctl() error -- Could not retrieve disk size."

IMHO the root cause is that the installer uses fdasd/dasdfmt for all dasd devices.
Sounds right, but isn't always :-/

If the dasd is a FBA dasd - like in this case - it is not working in the usual track/record mode, but instead in fixed blocks.

That can be checked in the install environment per disk e.g.:
~ # cat /sys/block/dasda/device/discipline
FBA

If preferred one can also use "lszdev" for that check. Start on "--list-types" on page 408 on http://public.dhe.ibm.com/software/dw/linux390/docu/l4n4dd29.pdf. From there one can find how to get device info do via lszdev. E.g. parsing output from "lszdev -i 0.0.0106", but IMO the kernel interface should be more stable and realiable.

Be Aware:
See page 159 in http://public.dhe.ibm.com/software/dw/linux390/docu/l4n4dd29.pdf
We can see that FBA devices don't support CDL/LDL formatting and also can't be formatted by Linux itself.
Instead the documentation refers to "z/VM tools".
So be aware that Linux can't "fix up" a not yet formatted FBA-dasd.

jfh can share a bit about formatting them via z/VM if needed by anybody.
As a starter one might look at http://www.vm.ibm.com/devpages/ALTMARKA/diskfmt.html

In general handling is similar, but not always the same:
Enabling (the same)
$ sudo chzdev -e 0.0.0106
FBA DASD 0.0.0106 configured

Display (the same, but watch the Type column)
$ lsdasd -a
Bus-ID Status Name Device Type BlkSz Size Blocks
==============================================================================
0.0.0200 active dasda 94:0 ECKD 4096 7042MB 1802880
0.0.0106 active dasdd 94:12 FBA 512 65535MB 134217724

Partitioning (different)
fdisk (like on scsi luns, instead of fdasd as on dasd's)

Afterwards everything is the same again for all devices as form now on it is a linux blockdev.

TODO (IMHO):
- fix installer to recognize and handle FBA-dasd's special
- add to documentation that FBA dasds have to be pre-formatted by the user via z/VM tools referring to IBM doc

Just looked a bit with jfh who prepped a similar setup - thanks.
jfh found some issues when recreating like: "fdasd: ioctl() error -- Could not retrieve disk size."

IMHO the root cause is that the installer uses fdasd/dasdfmt for all dasd devices.
Sounds right, but isn't always :-/

If the dasd is a FBA dasd - like in this case - it is not working in the usual track/record mode, but instead in fixed blocks.

That can be checked in the install environment per disk e.g.:
~ # cat /sys/block/dasda/device/discipline 
FBA

If preferred one can also use "lszdev" for that check. Start on "--list-types"  on page 408 on http://public.dhe.ibm.com/software/dw/linux390/docu/l4n4dd29.pdf. From there one can find how to get device info do via lszdev. E.g. parsing output from "lszdev -i 0.0.0106", but IMO the kernel interface should be more stable and realiable.

jfh can share a bit about formatting them via z/VM if needed by anybody.
As a starter one might look at http://www.vm.ibm.com/devpages/ALTMARKA/diskfmt.html

In general handling is similar, but not always the same:
Enabling (the same)
$ sudo chzdev -e 0.0.0106
FBA DASD 0.0.0106 configured

Display (the same, but watch the Type column)
$ lsdasd -a
Bus-ID     Status      Name      Device  Type  BlkSz  Size      Blocks
==============================================================================
0.0.0200   active      dasda     94:0    ECKD  4096   7042MB    1802880
0.0.0106   active      dasdd     94:12   FBA   512    65535MB   134217724

Partitioning (different)
fdisk (like on scsi luns, instead of fdasd as on dasd's)

Afterwards everything is the same again for all devices as form now on it is a linux blockdev.

TODO (IMHO):
- fix installer to recognize and handle FBA-dasd's special
- add to documentation that FBA dasds have to be pre-formatted by the user via z/VM tools referring to IBM doc