More info in case there are any reiserfs gurus out there. Found a piece of log from an earlier boot when it actually mounted ok. I cannot understand what changes can have happened except filling up lots of the space...

Dec 27 18:39:29 somebox kernel: sdc : very big device. try to use READ CAPACITY(16).
Dec 27 18:39:29 somebox kernel: SCSI device sdc: 4374845440 512-byte hdwr sectors (2239921 MB)
Dec 27 18:39:29 somebox kernel: SCSI device sdc: drive cache: none
Dec 27 18:39:29 somebox kernel:  sdc: sdc1
Dec 27 18:39:31 somebox kernel: sdc : very big device. try to use READ CAPACITY(16).
Dec 27 18:39:31 somebox kernel: SCSI device sdc: 4374845440 512-byte hdwr sectors (2239921 MB)
Dec 27 18:39:31 somebox kernel: SCSI device sdc: drive cache: none
Dec 27 18:39:31 somebox kernel:  sdc: sdc1
Dec 27 18:42:15 somebox kernel: ReiserFS: sdc1: using ordered data mode
Dec 27 18:42:15 somebox kernel: ReiserFS: sdc1: journal params: device sdc1, size 8192, journal first block 18, max trans len 1024, max batch 900, max commit age 30, max trans age 30
Dec 27 18:42:15 somebox kernel: ReiserFS: sdc1: checking transaction log (sdc1)
Dec 27 18:42:16 somebox kernel: ReiserFS: sdc1: Using r5 hash to sort names

Regards,
Harald