This was overcome by ext4 filesystem theoritically supporting maximum filesystem size of 1EB (1 million TB i.e 1 EB = 1024 PB, 1 PB = 1024 TB, 1 TB = 1024 GB). One of the most important limitation of ext3 was 16TB filesystem size since it was using 32-bit block numbers and has a default 4k block size. So for 100MB file 100*1024/4 = 25600 blocksġ extent can represent upto 128MB so a single extent can be used for mappingĮxtents bring about a 25% throughput gain in large sequential I/O workloads when compared with ext3 hence increasing the overall performance of the filesystem. Using indirect block mapping schecme, 1 block = 4KB A single extent in ext4 can represent up to 128 MB An extent is a single descriptor that represents a range of contiguous blocks. NOTE: Ext4 is available from machines having kernel version 2.6.19 Extent SupportĮxt3 filesystem was designed to use indirect block mapping scheme, which is efficient for small files but causes high metadata over head and poor performance when dealing with large files especially while performing delete or truncate operations because the mapping keeps a entry for every single block, and big files have many blocks which will led to huge mappings that will be slow to handle.Ī new feature called extent has been added to ext4 filesystem. In this article I will try to be very thorough mentioning the details of the features where ext3 lacked and ext4 helped overcoming to it. Ext3 was considered to be one of the most popular filsystems and is used in many commercial distributions but still with the increasing demands of the IT industry we started to find a lot of features which was lacking in ext3 which led to the development of ext4 filesystem.
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