For what reasons can the partition table go astray?

Question

linux

The server worked fine (Debian 7, RAID 1 software), decided to perform a dest-upgrade and then rebooted the server.
And everything flew.
Testdisk /debug /log result:

/dev/sdb: user_max 1465149168 sectors
/dev/sdb: native_max 1465149168 sectors
/dev/sdb: dco 1465149168 sectors
Warning: can't get size for Disk /dev/mapper/control - 0 B - CHS 1 1 1, sector size =512
Warning: can't get size for Disk /dev/md - 0 B - CHS 1 1 1 (RO), sector size=512
Hard disk list
Disk /dev/sda - 750 GB / 698 GiB - CHS 91201 255 63 , sector size=512 - WDC WD7500AALX-009BA0, S/N:WD-WCATR7026938, FW:15.01H15
Disk /dev/sdb - 750 GB / 698 GiB - CHS 91201 255 63, sector size=512 - WDC WD7500AALX-009BA0, S/N:WD-WCATR6903897, FW:15.01H15
Partition table type (auto): Intel
Disk /dev/sda - 750 GB / 698 GiB - WDC WD7500AALX-009BA0
Partition table type: Intel
Analyze Disk /dev/sda - 750 GB / 698 GiB - CHS 91201 255 63
Current partition structure:
Partition sector doesn't have the endmark 0xAA55
Ask the user for vista mode
Allow partial last cylinder : No
search_vista_part: 0
search_part()
Disk / dev/sda - 750 GB / 698 GiB - CHS 91201 255 63
Results
interface_write()
No partition found or selected for recovery
simulate write!
write_mbr_i386: starting...
write_all_log_i386: starting...
No extended partition
TestDisk exited normally.

fdisk-l:

Disk /dev/sda: 750.2 GB, 750156374016 bytes
81 heads, 63 sectors/track, 287115s, total 1465149168 sectors cylinder
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/ O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x9f0f7cc9
Device Boot Start End Blocks Id System
/dev/sda1 2048 1465149167 732573560 83 Linux
Disk /dev/sdb: 750.2 GB, 750156374016 bytes
81 heads, 63 sectors/ track, 287115 cylinders, total 1465149168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x202a7e6c
Device Boot Start End Blocks Id System
/dev/sdb1 2048 1465149167 732573560 83 Linux

What could have caused this?

Answer 1

Specify, does raid1 consist of entire disks (/dev/sda, /dev/sdb) or only the first partitions (/dev/sda1, /dev/sdb1)?
It would be nice to see the output of mdadm -D /dev/md*