hpr-knowledge-base/hpr_transcripts/hpr1550.txt

Episode: 1550
Title: HPR1550: The Ext3 and 4 File System
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr1550/hpr1550.mp3
Transcribed: 2025-10-18 04:57:18

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How dare you.
Okay guys, I hope you're having a great day.
Continuing my series of talks about the file systems, okay?
So in our last episode we talked about journaling file systems and there are a plethora of these
journaling things.
The most popular, at least in Linux, are XT3 and XT4, okay?
XT3 and XT4 are pretty famous because they're backward compatible with XT2, right?
And I still use XT2 with SD cards and things that don't require this journaling feature
all the time with me.
So the XT3 file system was added to Linux in 2001 and up until recently it was to default
the file systems in just about every Linux distribution.
It uses the same in no table and structure as XT2 but adds a journal system to each storage
device to journal the data written to the storage device.
Not to fault the XT system uses an ordered mode method of journaling, only writing the
in-note information to the journal file, but not removing it until the data blocks have
been successfully written to the storage device.
You can change the journaling method and use in the XT3 file system to either data or
write back modes with a simple command line option when creating the file system.
While XT3 file system added basic journaling to the Linux system, there were still a few
things that lacked.
For example, the XT3 system doesn't provide any recovery from incidental deletion files.
There's no built-in data compression available, although there's a patch that can be installed
separately that provides this feature.
And the XT file system doesn't support encrypting files.
For those reasons, the developers have chosen to continue work on improving the XT file
system.
And it works when compared to the XT2, which did two terabytes or 32 terabytes at the end.
The KIB block size ranges from 16 gigabytes to two terabytes.
And the file system size goes from two terabytes to 32 terabytes.
Now, the thing is with XT3 that in the enterprise space, believe it or not, 32 terabytes is not
enough in the enterprise often.
And so this is a severe limitation.
So this time, we're going to also do the XT4 because it's sort of the same, the XT file
thing.
And it's relatively short, the XT4.
So the XT4 is a result of expanding the XT3 file system.
As you probably guessed, the XT4 file system was visually supported in 2008.
And it's now the default system in many Linux distributions for the world going to XT4
file system can support volumes up to one extra byte.
And file size is up to 16 terabytes, T-I-B.
However, Red Hat recommends using XFS instead of XT4 for volumes larger than 100 terabytes.
And that's really interesting because, for instance, with HANA, SAP HANA, the XFS file
system is used by Sousa.
And I've heard that in Rail, Red Hat Enterprise Linux XFS will be the journaling thing.
And we'll talk about XFS in another one.
But it's important to note that even though XT4 really does some really fantastic things
that they've had to go back to XFS in the enterprise space because of the volumes, the
file volumes, 100 terabytes is just not enough, right?
Another neat thing with XT4 is the addition of compression and encryption.
The XT4 file system also supports a thing called extents.
This is allocation space on a storage device and blocks.
And only store the starting block in a location in the Inno table.
This helps save space in the Inno table by not having to list all of the data blocks
used to store the data from a file.
The XT4 system also incorporates a block pre-allocation.
If you want to reserve space on a storage device for a file you know will grow in size with
XT4 file system, it's possible to allocate all of the expected blocks to the file, not
just the blocks that physically exist.
XT4 file system fills in the reserve data blocks with zeros and it's not allowed to
allocate them to any other file.
Okay, so this pretty much includes the extended journaling file systems available on Linux.
Now for XT2 and XT3 I have a tool that lets me read like external hard drives that I
formatted in XT2 or XT3 in Windows.
And I haven't seen one for XT4 yet but I'm pretty sure that that'll happen.
Okay, as always I really thank you and appreciate your time.
And if you have any questions you can reach me at JWP5 at hotmail.com.
Thank you very much.
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