It covers the main differences between ext3 and ext4 with a focus on filesystem consistency. This article was the initial motivation of this blog series, because many engineers are unaware that the standard option of ext4 (delalloc) is dangerous for their data! 4.1 Main differences Ext3 was available since 2001 with Linux Kernel 2.4.15 and […]
This blog article details how a brutal interruption of a write operation can corrupt a whole filesystem and how a journal provides a protection against such incomplete writes. 3.1 Consequences of uncomplete writes When you write a file, the underlying filesystem is actually doing two different kinds of write operations: metadata and data writes. For […]
This article aims to give a clear representation of the relation between filenames and inodes, to explain what is an inode and which differences exist between a hard link and a symbolic link. 2.1 Filename as Hardlink to Inode On ext3 and ext4 (and some other filesystems) a file is stored internally as an inode […]
It explains how files are split into blocks and how the filesystem acts as an abstraction layer between files (seen by applications) and blocks (physically written on disks). It also says why disks are called block devices. 1.1 Splitting Up Files Into Blocks A block device is a storage media, like a hard disk. You […]
This blog series aims to be a reference guideline by collecting useful knowledge and tutorials about Linux filesystems, mainly about ext3 and ext4. Because, as systems engineers/administrators, when we need to manually perform disk maintenance on a server, we know that a tiny mistake may have large consequences. “Trial-and-Error” is sometimes a good way to […]
Introduction Your Linux servers are running smoothly? Fine.Now if something incidentally gets wrong you need also to prepare an emergency plan.And even when everything is going fine, a backup that is directly stored on the same server can still be useful: for example when you need to see what was changed on a specific file, […]