www.lakat.eu

Tape Drive

Usage

To initialize the drive, you want to:

stinit

To rewind the tape, do

mt -f /dev/nst0 rewind

To write data to it, do

tar cvf /dev/nst0 archive2/

To read data, do

tar xvf /dev/nst0

[root@kazi restore]# mt -f /dev/nst0 rewind
[root@kazi restore]# mt -f /dev/nst0 tell
At block 0.
[root@kazi restore]# tar -tf /dev/nst0
archive1/
archive1/1.MTS
[root@kazi restore]# mt -f /dev/nst0 tell
At block 22168.
[root@kazi restore]# tar -tf /dev/nst0
archive2/
archive2/2.MTS
[root@kazi restore]# mt -f /dev/nst0 tell
At block 44336.

Now rewinding

[root@kazi restore]# mt -f /dev/nst0 bsf 1
[root@kazi restore]# mt -f /dev/nst0 tell
At block 44335.
[root@kazi restore]# mt -f /dev/nst0 bsf 1
[root@kazi restore]# mt -f /dev/nst0 tell
At block 22167.
[root@kazi restore]# mt -f /dev/nst0 fsf 1
[root@kazi restore]# mt -f /dev/nst0 tell
At block 22168.
[root@kazi restore]# tar -tf /dev/nst0
archive2/
archive2/2.MTS

So if you are at the end of the drive:

[root@kazi restore]# mt -f /dev/nst0 bsf 2
[root@kazi restore]# mt -f /dev/nst0 fsf 1
[root@kazi restore]# mt -f /dev/nst0 tell
At block 22168.

System V semantics

[root@kazi ~]# tar cvf /dev/nst0 archive1
archive1/
archive1/1.MTS
[root@kazi ~]# tar cvf /dev/nst0 archive2
archive2/
archive2/2.MTS
[root@kazi ~]# tar cvf /dev/nst0 archive3
archive3/
archive3/3.MTS
[root@kazi ~]# mt -f /dev/nst0 tell
At block 66504.

[root@kazi ~]# mt -f /dev/nst0 rewind
[root@kazi restore]# tar xvf /dev/nst0
archive1/
archive1/1.MTS
[root@kazi restore]# mt -f /dev/nst0 tell
At block 22168.
[root@kazi restore]# tar xvf /dev/nst0
archive2/
archive2/2.MTS
[root@kazi restore]# mt -f /dev/nst0 tell
At block 44336.
[root@kazi restore]# tar xvf /dev/nst0
archive3/
archive3/3.MTS
[root@kazi restore]# mt -f /dev/nst0 tell
At block 66504.

Timing:

time tar cvf /dev/nst0 /data/tape1/
...
real    57m7.877s
user    1m16.384s
sys 9m57.844s
[root@kazi restore]# #time tar cvf /dev/nst0 /data/tape1/
[root@kazi restore]# du -shc /data/tape1/
265G    /data/tape1/
265G    total

Doing it again:

real    54m32.163s
user    1m13.405s
sys 9m55.750s
[root@kazi ~]# time tar cvf /dev/nst0 /data/tape1/

Restore

real    62m12.270s
user    1m22.551s
sys 19m14.131s
[root@kazi restore]# time tar -xvf /dev/nst0

Get some stats:

[ormester@kazi ITDT]$ sudo sg_logs -a /dev/nst0 | less

Another useful link: https://darkimmortal.com/adventures-with-lto-tape-for-home-casual-use/

Let's try to rewind

The maintained source code for mt-st is here: https://github.com/iustin/mt-st

To initialise it we'll need an stinit.def file

https://wiki.debian.org/StinitDef

My tape drive looks like this:

[ormester@kazi ~]$ sudo lsscsi
[0:0:0:0]    tape    IBM      ULTRIUM-HH5      F991  /dev/st0 
[1:2:0:0]    disk    DELL     PERC H710        3.13  /dev/sda 
[1:2:1:0]    disk    DELL     PERC H710        3.13  /dev/sdb

The used config is /etc/stinit.def - which was taken from here: https://wiki.debian.org/StinitDef#LTO5

manufacturer="IBM" model = "ULTRIUM-HH5" {
scsi2logical=1
can-bsr=1
auto-lock=1
two-fms=0
drive-buffering=1
buffer-writes
read-ahead=1
async-writes=1
can-partitions=1
fast-mteom=0
sysv=1
#
# If your stinit supports the timeouts:
timeout=180 # 3 minutes
long-timeout=14400 # 4 hours
#
mode1 blocksize=0 compression=0 # 1500 GB, LTO5 _NO_ compression
mode2 blocksize=0 compression=1 # 3000 GB, LTO5 compresses
mode3 disabled=1
mode4 disabled=1
}

Having said that, I found some entries who were suggesting slightly different config, which has a slight difference

sysv=0
sili=1

instead of

sysv=1

What that means is

sili=value If value is non-zero, the SILI bit is set when reading in variable block mode. This may speed up reading blocks shorter than the read byte count. Set this only if you know that the drive supports SILI and the HBA reliably returns transfer residual byte counts. Requires kernel version >= 2.6.26.

And the other setting

sysv=value The System V tape semantics are used if value is non-zero. Otherwise the BSD semantics are used.

More about it here: https://www.kernel.org/doc/html/latest/scsi/st.html#bsd-and-sys-v-semantics9

The user can choose between these two behaviours of the tape driver by defining the value of the symbol ST_SYSV. The semantics differ when a file being read is closed. The BSD semantics leaves the tape where it currently is whereas the SYS V semantics moves the tape past the next filemark unless the filemark has just been crossed.

Initialization of the drive was performed by:

Bacula was helpful: https://www.bacula.org/5.2.x-manuals/en/problems/problems/Testing_Your_Tape_Drive.html

Also this one: https://wiki.zmanda.com/index.php/Tape_Driver_Semantics

https://www.techtarget.com/searchdatabackup/definition/shoeshining-or-backhitching

The command:

tar -b 4096 -cvf - agica-hdd/ | mbuffer -m 4G -L -P 95 -f | dd of=/dev/nst0 bs=2M iflag=fullblock

[root@kazi tape1]# find -mindepth 1 -type d -exec sh -c "cd {}; md5sum * > md5sums.txt" \;

sg_logs -a /dev/nst0 > tepe1.sglogs