What is a volume bitmap?
Volume bitmap is an array of bits that tracks which blocks are in use and which are free.
Let’s interpret couple bitmap log messages
First line suggests, it encountered an I/O error trying to read block bitmap. Typically this mean, there is either a problem with the connection from the computer/vm/server to the storage or volume is severely corrupted.
Second line suggests, it’s a delayed block allocation failure, which mean it tried to write data to a file, but ext4 couldn’t allocate a block. Also it informs error -5, which is EIO – I/O error [Tip: Do you know, Linux calls will return file handles as positive numbers, and represent errors by returning a negative number)
Now, it’s time for a question (~!~)
-> When a write call occours, does it read bitmap for every call?
No, it’s cached in RAM. It has to be written when blocks are allocated.