Odd De-compression CRC error on new Mint 19r3 with 5.3.0-45-generic kernel

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Odd De-compression CRC error on new Mint 19r3 with 5.3.0-45-generic kernel

Tim Jones
Hi Mark,

I hope you're staying safe and well.  We're all on lock-down here, so I'm running a load of Linux system tests.

I built a fresh Mint 19.3 system and am running into the following error when trying to read a loaded tape after it was written:

[80214.774942] st 16:0:0:0: [st0] Sense Key : Medium Error [current] 
[80214.774944] st 16:0:0:0: [st0] Add. Sense: De-compression CRC error
[81293.781471] st 16:0:0:0: [st0] Sense Key : Medium Error [current] 
[81293.781475] st 16:0:0:0: [st0] Add. Sense: De-compression CRC error
[81590.733122] st 16:0:0:0: [st0] Sense Key : Medium Error [current] 
[81590.733124] st 16:0:0:0: [st0] Add. Sense: De-compression CRC error
[81671.512809] st 16:0:0:0: [st0] Sense Key : Medium Error [current] 
[81671.512815] st 16:0:0:0: [st0] Add. Sense: De-compression CRC error
[81734.053362] st 16:0:0:0: [st0] Sense Key : Medium Error [current] 
[81734.053370] st 16:0:0:0: [st0] Add. Sense: De-compression CRC error

The "data" file is correct and not corrupt because I can read it as a disk archive with BRU and our internal 32bit CRC values are correct.

Here's my library.conf file:

VERSION: 5

# VPD page format:
# <page #> <Length> <x> <x+1>... <x+n>
# NAA format is an 8 hex byte value seperated by ':'
# Note: NAA is part of inquiry VPD 0x83
#
# Each 'record' is separated by one (or more) blank lines.
# Each 'record' starts at column 1
# Serial num max len is 10.
# Compression: factor X enabled 0|1
#     Where X is zlib compression factor	1 = Fastest compression
#						9 = Best compression
#     enabled 0 == off, 1 == on
#
# fifo: /var/tmp/mhvtl
# If enabled, data must be read from fifo, otherwise daemon will block
# trying to write.
# e.g. cat /var/tmp/mhvtl (in another terminal)

Library: 10 CHANNEL: 00 TARGET: 00 LUN: 01
 Vendor identification: TOLISGRP
 Product identification: TGL2240
 Unit serial number: MX700192AG
 NAA: 10:22:33:44:ab:00:00:00
 Home directory: /opt/mhvtl
 PERSIST: False
 Backoff: 400
# fifo: /var/tmp/mhvtl

Drive: 11 CHANNEL: 00 TARGET: 00 LUN: 00
 Library ID: 10 Slot: 01
 Vendor identification: TOLISGRP
 Product identification: ULTRIUM-HH7
 Unit serial number: HU009128S3
 NAA: 10:22:33:44:ab:00:01:00
 Compression: factor 1 enabled 0
 Compression type: lzo
 Backoff: 400
# fifo: /var/tmp/mhvtl

As you can see, I've disabled compression because I'm working with large (10GB+ media files) and teh write is successful and not compressed, so I'm not sure why the reader is trying to decompress the data from the written tape.

Ideas?
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Re: Odd De-compression CRC error on new Mint 19r3 with 5.3.0-45-generic kernel

Tim Jones
It turns out that this occurs when trying to perform a read from the virtual volume at a block size that is smaller (or not a larger multiple of) the block size used when the volume was written.

The Linux kernel supports short reads from tape when the drive is in variable block mode.  The reference is MT_ST_SILI in the st driver.