I am experimenting with some old SCSI tape drives, and I have successfully written some data to a tape, but I am struggling trying to read it back again.
# tar tvf /dev/st0 tar: /dev/st0: Cannot read: Cannot allocate memory tar: At beginning of tape, quitting now tar: Error is not recoverable: exiting now # dd if=/dev/st0 of=test dd: error reading '/dev/st0': Cannot allocate memory 0+0 records in 0+0 records out 0 bytes copied, 3.20155 s, 0.0 kB/s
After these commands,
st 10:0:3:0: [st0] Block limits 1 - 16777215 bytes. st 10:0:3:0: [st0] Failed to read 65536 byte block with 512 byte transfer. st 10:0:3:0: [st0] Failed to read 131072 byte block with 65536 byte transfer. st 10:0:3:0: [st0] Failed to read 65536 byte block with 10240 byte transfer. st 10:0:3:0: [st0] Failed to read 94208 byte block with 69632 byte transfer. st 10:0:3:0: [st0] Failed to read 65536 byte block with 10240 byte transfer. st 10:0:3:0: [st0] Failed to read 65536 byte block with 512 byte transfer.
Most of these were because I was testing different block sizes with the
tar -b option, but none of those had any effect.
Occasionally I'm able to read a few kB of data off the first block on the tape (which tar can extract until the data cuts off), but usually it fails with no data at all read.
I have (apparently) successfully written data to tape, moved the tape to the other drive, seeked to the end of the data and then written more, so there appears to be no difficulty in writing data to the drive, just in reading it back again.
I am using two LTO-3 drives. One is a half height HP Ultrium 920 and the other is a full height HP Ultrium 960. Both of them have this problem. I have tried with two different SCSI cards (an LSI Logic Ultra320 card and an Adaptec Ultra2/SE 40MB/sec card), both of which produce the same errors.
I have tried a cable with an attached terminator (gave me 40MB/sec even on the Ultra320 card), then a two-connector cable which meant I could only connect one drive so I enabled the "term power" jumper on the drive, which got me to Ultra160 (even though the drive and controller are both Ultra320) but none of this changed anything and throughout it all I still got the same errors when trying to read from the drive.
I downgraded from Linux kernel 4.10.13 to 4.4.3 (the previous version on this machine) and the error message changes from "Cannot allocate memory" to "Input/output error" but the problem remains the same.
Any ideas what could cause this error?
EDIT: The 40MB/sec problem was caused because I was using an SE active terminator. Once I replaced this with an LVD terminator the speeds went up to Ultra160. I think I need new cables to hit Ultra320 but this is now double the tape bandwidth (max 80MB/sec) so it's fine with me for the time being. Made no difference with the error messages though.