ext4

I know that my question has an answer here: QFile seek performance . But I am not completely satisfied with the answer. Even after looking at the following implementation of generic_file_llseek() for ext4, I can't seem to understand how can the complexity be measured. /** * generic_file_llseek - generic llseek implementation for regular files * @file: file structure to seek on * @offset: file offset to seek to * @origin: type of seek * * This is a generic implemenation of ->llseek useable for all normal local * filesystems. It just updates the file offset to the value specified by * @offset

I am writing a library that uses the Linux asynchronous I/O system calls, and would like to know why the io_submit function is exhibiting poor scaling on the ext4 file system. If possible, what can I do to get io_submit not to block for large IO request sizes? I already do the following (as described here ): Use O_DIRECT . Align the IO buffer to a 512-byte boundary. Set the buffer size to a multiple of the page size. In order to observe how long the kernel spends in io_submit , I ran a test in which I created a 1 Gb test file using dd and /dev/urandom , and repeatedly dropped the system cache

I'm writing an app that needs to store lots of files up to approx 10 million. They are presently named with a UUID and are going to be around 4MB each but always the same size. Reading and writing from/to these files will always be sequential. 2 main questions I am seeking answers for: 1) Which filesystem would be best for this. XFS or ext4? 2) Would it be necessary to store the files beneath subdirectories in order to reduce the numbers of files within a single directory? For question 2, I note that people have attempted to discover the XFS limit for number of files you can store in a single

A while back I bought a 1TB USB external drive. I formatted it ext4 in Ubuntu and copied a bunch of files / folders to it from several machines, all to /home/machinename/whatever, respectively. At some point I ran a chmod -R shell command on it to change the permissions. That was months ago and I don't remember what I typed but it made the drive so I could only access its /home folder as root. This wasn't a problem because I could still access everything, but today I decided to try to fix it. I went to my shell as root, went to that drive and typed: chown -R rick:rick ./ chmod -R 666 ./ It

What's the correct way to durably rename a file in a POSIX file system? Specifically wondering about fsyncs on the directories . (If this depends on the OS/FS, I'm asking about Linux and ext3/ext4). Note : there are other questions on StackOverflow about durable renames, but AFAICT they don't address fsync-ing the directories (which is what matters to me - I'm not even modifying file data). I currently have (in Python): dstdirfd = open(dstdirpath, O_DIRECTORY|O_RDONLY) rename(srcdirpath + '/' + filename, dstdirpath + '/' + filename) fsync(dstdirfd) Specific questions : Does this also

A very basic question. What is the exact sequence of steps executed when I try to open a file-descriptor, by providing fully-qualified path to the file. I am looking for how this works on Linux given a file name - how is it translated to inode and disk-sector does linux file system (specifically ext3 and ext4) maintain some kind of filename to inode mapping? Basile Starynkevitch In addition of tmp's answer : Files really are inodes . Usually, a given file has some entry in some directory pointing to its inode. Directories are mapping names to inodes, and directories are a kind of file. See