LTO4 cartrige erase: what's the reasonable time to complete?

kaza · 09-11-2021, 08:05 AM

Hello!

Two days ago I started multi-volume backup (by tar) to 3 LTO4 cartriges, 800GB each.
In a separate shell I'm running from time to time a script which parses the "tar" STDOUT
redirection file and reports how much data had been backed up in total and how much since the last
volume change.

After the first cartrige filled up I replaced it with the second, hit "Enter" and the backup continued.
But, unexpectedly, after backing up just 7GB (instead of 800GB) to the second volume, it paused again
with "Prepare volume ... and hit return". I decided to stop the backup process, run status on the
second volume carttige:

Code:

<root localhost>.../backup>mt -f /dev/st0 status
SCSI 2 tape drive:
File number=0, block number=0, partition=0.
Tape block size 0 bytes. Density code 0x46 (LTO-4).
Soft error count since last status=0
General status bits on (41010000):
 BOT ONLINE IM_REP_EN

After that I decided to erase the second volume and to repeat the backup process.
I started: "mt -f /dev/st0 erase" yesterday at about 16:00.
I expected it to take few hours (from what I've read expected time for "erase"
varied from 4 to 6 hours) but I'm already approaching to 24 hours and it's still running
(the tape "Ready" LED blinks and I can hear its motor spinning).
On my desktop there are "gkrellm" monitors and when the PC is idle, the disk monitor shows
throughput of about 2-3 kB/Sec which is a far cry from the SAS capability (the disks and the tape
are connected to a SAS controller (Adaptec ICP 5165BR). From what I'be read the command
"mt -f /dev/st0 erase" fills the cartrige with some constant value, although I don't know
if it actually writes all this data (which would be seen as high throughput activity) or just
instructs the tape to write oven and over the hardcoded inside the tape constant (in which case almost no throughput would be monitored).

Can anyone share their experience of how long it took them to complete this command?
I have one more unused cartrige so if I'll decide that the "erase" is doing something totally wrong I'll stop it (which'll make the currently used cartrige unusable) and use the spare one but before
using such drastic measures I want to be sure something is really wrong. Maybe 24 hours (or slightly
more) is actually a reasonable time for this command to complete and I just have to wait a little more?

TIA,
kaza.

wpeckham · 09-11-2021, 09:13 AM

I have seen full tape erase take quite a long time, but that sounds like a bad tape. I would swap it out for a new one and see if that works better.

Do you track usage? That tape has (if memory serves, and it HAS been a long time) about 400 writes of life. An erase counts as a write. A prep counts as a write. a backup counts as a write. If it has been in use long enough to have been written over 390 times, it may be EOL. If it is new, it may have a MFG flaw.

kaza · 09-16-2021, 12:47 AM

Thanks for the reply (and sorry for me taking long to re-reply, life etc.)

It took about 31 hours for the erase to complete. After that I tried the same "status" command and instead of completing in a second
it took few hours. Luckily, I had one more cartrige so I marked the problematic one as "bad" and started using another one.
The cartriges didn't have that many writes on them: I have 3 sets of 3 cartriges which I rotate and each set had been written only twice
since I bought it so it looks more like a manufacturing defect.