The raid controller went RO due to a drive bug, umount read:

[2241330.149540] lost page write due to I/O error on sdb
[2241330.149597] EXT4-fs error (device sdb): ext4_put_super:819: Couldn't clean up the journal

Upon starting Maria:

121220 17:07:54 mysqld_safe Starting mysqld daemon with databases from /vol/mysql/data
121220 17:07:55 [Warning] /vol/mysql/bin/mysqld: ignoring option '--character-set-client-handshake' due to invalid value 'utf8'
/vol/mysql/bin/mysqld: Query cache is disabled (resize or similar command in progress); repeat this command later
InnoDB: Warning: innodb_log_block_size has been changed from default value 512. (###EXPERIMENTAL### operation)
InnoDB: The log block size is set to 4096.
121220 17:07:55 InnoDB: The InnoDB memory heap is disabled
121220 17:07:55 InnoDB: Mutexes and rw_locks use GCC atomic builtins
121220 17:07:55 InnoDB: Compressed tables use zlib 1.2.3
121220 17:07:55 InnoDB: Using Linux native AIO
121220 17:07:55 InnoDB: Initializing buffer pool, size = 48.8G
121220 17:07:59 InnoDB: Completed initialization of buffer pool
121220 17:07:59 InnoDB: highest supported file format is Barracuda.
InnoDB: Log scan progressed past the checkpoint lsn 3450267893160
121220 17:08:00 InnoDB: Database was not shut down normally!
InnoDB: Starting crash recovery.
InnoDB: Reading tablespace information from the .ibd files...
InnoDB: Restoring possible half-written data pages from the doublewrite
InnoDB: buffer...
InnoDB: Doing recovery: scanned up to log sequence number 3450269696739
121220 17:08:05 InnoDB: Assertion failure in thread 140671431432000 in file trx0undo.c line 775
InnoDB: Failing assertion: mach_read_from_2(undo_page + TRX_UNDO_PAGE_HDR + TRX_UNDO_PAGE_TYPE) == TRX_UNDO_INSERT
InnoDB: We intentionally generate a memory trap.
InnoDB: Submit a detailed bug report to http://bugs.mysql.com.
InnoDB: If you get repeated assertion failures or crashes, even
InnoDB: immediately after the mysqld startup, there may be
InnoDB: corruption in the InnoDB tablespace. Please refer to
InnoDB: http://dev.mysql.com/doc/refman/5.5/en/forcing-innodb-recovery.html
InnoDB: about forcing recovery.
121220 17:08:05 [ERROR] mysqld got signal 6 ;
This could be because you hit a bug. It is also possible that this binary
or one of the libraries it was linked against is corrupt, improperly built,
or misconfigured. This error can also be caused by malfunctioning hardware.

To report this bug, see http://kb.askmonty.org/en/reporting-bugs

We will try our best to scrape up some info that will hopefully help
diagnose the problem, but since we have already crashed,
something is definitely wrong and this may fail.

Server version: 5.5.28-MariaDB-log
key_buffer_size=16777216
read_buffer_size=262144
max_used_connections=0
max_threads=501
thread_count=0
It is possible that mysqld could use up to
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 1174932 K bytes of memory
Hope that's ok; if not, decrease some variables in the equation.

Thread pointer: 0x0x0
Attempting backtrace. You can use the following information to find out
where mysqld died. If you see no messages after this, something went
terribly wrong...
stack_bottom = 0x0 thread_stack 0x48000
mysys/stacktrace.c:247(my_print_stacktrace)[0xaadcfe]
sql/signal_handler.cc:153(handle_fatal_signal)[0x6e5e82]
:0()[0x7ff09e71acb0]
:0()[0x7ff09d741425]
:0()[0x7ff09d744b8b]
trx/trx0undo.c:773(trx_undo_insert_header_reuse)[0x8ae179]
trx/trx0undo.c:730(trx_undo_parse_page_header)[0x8ae94d]
log/log0recv.c:1230(recv_parse_or_apply_log_rec_body)[0x950ff2]
log/log0recv.c:1677(recv_recover_page_func)[0x952a32]
buf/buf0buf.c:4089(buf_page_io_complete)[0x8d8b6f]
buf/buf0rea.c:256(buf_read_page_low)[0x8ec6d1]
buf/buf0rea.c:458(buf_read_page)[0x8edcb9]
buf/buf0buf.c:2590(buf_page_get_gen)[0x8dcf9e]
include/trx0undo.ic:159(trx_undo_page_get)[0x8af11c]
trx/trx0rseg.c:225(trx_rseg_mem_create)[0x8a3f22]
trx/trx0rseg.c:301(trx_rseg_create_instance)[0x8a4547]
trx/trx0sys.c:1284(trx_sys_init_at_db_start)[0x8a7415]
srv/srv0start.c:1906(innobase_start_or_create_for_mysql)[0x893465]
handler/ha_innodb.cc:2998(innobase_init)[0x8534bc]
sql/handler.cc:469(ha_initialize_handlerton(st_plugin_int*))[0x6e7518]
sql/sql_plugin.cc:1354(plugin_initialize)[0x59d65c]
sql/sql_plugin.cc:1595(plugin_init(int*, char**, int))[0x59e649]
sql/mysqld.cc:4297(init_server_components)[0x50c791]
sql/mysqld.cc:4855(mysqld_main(int, char**))[0x50d4eb]
:0()[0x7ff09d72c76d]
??:0(_start)[0x503259]
The manual page at http://dev.mysql.com/doc/mysql/en/crashing.html contains
information that should help you find out what is causing the crash.
121220 17:08:07 mysqld_safe mysqld from pid file /tmp/mysqld.pid ended