Data file write failure for LTO-6 drives about mhvtl

[markh794]

Hello Peter,

Can I enquire as to the underlying file system on /opt/mhvtl - is it ext3,4,xfs etc and if the underlying block device is 'local' or nfs/cifs etc.

[rohr22]

Hi, Mark.

It is ext4. We put our mhvtl tape volume files under the old default directory of /opt/vtl. The disk where the files reside is local. We used a opt-vtl.mount file under the /etc/systemd/system directory to mount the disk to the /opt/vtl directory. It has these contents:

[Unit]
Description=MHVTL
[Mount]
What=/dev/disk/by-uuid/c1debf41-51c5-41dd-9b90-54d974e455b6
Where=/opt/vtl
Type=ext4
Options=defaults
[Install]
WantedBy=multi-user.target

Does that answer your questions?

Thank you,
Peter

[rohr22]

It seems like there might be issues with the latest mhvtl version and LTO-6 drives on RHEL8. I noticed that with mhvtl 1.6.4 the problems with LTO-6 drives don't occur on RHEL8. When I updated my system that has mhvtl 1.7.0 to use LTO-5 drives the problems did not occur. The only difference between what I was testing with before with mhvtl 1.7.0 was that the etc/generate_device_conf.in file had:

        add_library 10 0 0 0 "IBM" "3584"  "2160"  "XYZZY_A"
        #         index channel target LUN S/No Lib# Slot
        add_ibm_ultrium_5_drive 11 0 1 0 "XYZZY_A1" 10 1
        add_ibm_ultrium_5_drive 12 0 2 0 "XYZZY_A2" 10 2
        add_ibm_ultrium_5_drive 13 0 3 0 "XYZZY_A3" 10 3
        add_ibm_ultrium_5_drive 14 0 4 0 "XYZZY_A4" 10 4
        add_ibm_ultrium_5_drive 15 0 5 0 "XYZZY_A5" 10 5
        add_ibm_ultrium_5_drive 16 0 6 0 "XYZZY_A6" 10 6
        add_ibm_ultrium_5_drive 17 0 7 0 "XYZZY_A7" 10 7
        add_ibm_ultrium_5_drive 18 0 8 0 "XYZZY_A8" 10 8
        add_ibm_ultrium_5_drive 19 0 9 0 "XYZZY_A9" 10 9
        add_ibm_ultrium_5_drive 20 0 10 0 "XYZZY_AA" 10 10

instead of:

        add_library 10 0 0 0 "IBM" "3584"  "2160"  "XYZZY_A"
        #         index channel target LUN S/No Lib# Slot
        add_ibm_ultrium_6_drive 11 0 1 0 "XYZZY_A1" 10 1
        add_ibm_ultrium_6_drive 12 0 2 0 "XYZZY_A2" 10 2
        add_ibm_ultrium_6_drive 13 0 3 0 "XYZZY_A3" 10 3
        add_ibm_ultrium_6_drive 14 0 4 0 "XYZZY_A4" 10 4
        add_ibm_ultrium_6_drive 15 0 5 0 "XYZZY_A5" 10 5
        add_ibm_ultrium_6_drive 16 0 6 0 "XYZZY_A6" 10 6
        add_ibm_ultrium_6_drive 17 0 7 0 "XYZZY_A7" 10 7
        add_ibm_ultrium_6_drive 18 0 8 0 "XYZZY_A8" 10 8
        add_ibm_ultrium_6_drive 19 0 9 0 "XYZZY_A9" 10 9
        add_ibm_ultrium_6_drive 20 0 10 0 "XYZZY_AA" 10 10

Could there be something miscoded with the use of add_ibm_ultrium_6_drive vs add_ibm_ultrium_5_drive in the latest mhvtl version? (I used the zip file from the latest code as of June 5, 2022.)

Thank you,
Peter

[rohr22]

Note that the system with issues is a ppc64le system with RHEL 8.5. But I also seemed to have similar issues when the etc/generate_device_conf.in file had add_ibm_ultrium_6_drive calls on a RHEL 8.5 x86_64 system.

[markh794]

The read/write path is exactly the same for all 'emulations'.
The only difference in emulation is the MODE, LOG and INQUIRY (some emulations also include persistent SCSI reservation & Security Protocol IN/OUT) op codes.
Using the 'edit_tape' - you can flip the media type between LTO to DLT to AIT and successfully read/write the same media files from appropriate drive emulation.

[rohr22]

The only difference in emulation is the MODE, LOG and INQUIRY (some emulations also include persistent SCSI reservation & Security Protocol IN/OUT) op codes.

Could this account for the issues I am seeing with the drives created with add_ibm_ultrium_6_drive vs add_ibm_ultrium_5_drive?

[markh794]

No - LTO-4+ emulations all support the same PR & SPIN/SPOUT code.
I just checked (diff -u) the init_ult3580_td5 and init_ult3580_td6 functions and the mode pages and log pages are the same.
The only difference is the list of media permitted to be mounted :
LTO-3 R/O, LTO-4 & LTO-5 R/W for -TD5,
LTO-4 R/O, LTO-5 & LTO-6 R/W for -TD6
i.e. mhvtl code does not treat the two emulations any differently.

Is it possible the application expects the -TD5 / -TD6 to behave slightly differently - and my 'emulation' is incomplete ?

[rohr22]

There might be an issue with our hardware that is causing us issues. The mhvtl volumes seem to work fine for a while, but eventually we may run into the issues noted here on some of our machines. However, this can happen for both LTO-5 and LTO-6 drives.