[nknighthb]

> they use all of the space available to them equally (or, pseudorandomly anyway)

This is simply false for many (if not most) filesystems, which preferentially write to blocks near the beginning of the disk. For spinning disks, random distribution of blocks would kill performance.

[fuzzbang]

No, it is not false. The important thing with a spinning disk is locality of reference. You want the blocks which store the file content to be as close together as possible, to minimize the head seek times. This means you want as long a chain of contiguous blocks as possible. This does not mean that you want all those blocks to be at the beginning of the disk. In fact, the exact opposite. You want to start that chain at a random location so you are more likely to have a large number of contiguous unallocated blocks. See the implementation of HFS+ Extents, or Ext4, or UFS for examples of how this works.

[nknighthb]

A) You have forgotten basic physics. The beginning of the disk is faster. Locality is desirable but is not and has never been the only thing that matters.

B) You have just named three uncommon filesystems that few people will ever use in the first place, much less with TrueCrypt.

[nitrogen]

A) You have forgotten basic physics. The beginning of the disk is faster. Locality is desirable but is not and has never been the only thing that matters.

If you haven't actually looked at the block allocation patterns of common filesystems, then you can't say conclusively that fuzzbang is incorrect. Arguments from first principles (e.g. "basic physics") cannot override empirical evidence.

Further, locality of reference will have a much, much bigger influence on spinning disk I/O throughput than location at the front of the disk. The difference between the outer rim and inner rim might be 120MB/s to 70MB/s, so reading a contiguous 200MB file will take 1.7x as long if it's stored at the inner rim (286ms vs 167ms). However, if that 200MB file is stored in 100 2MB fragments, and seeking to each fragment takes 4ms, your reading time will be dominated by the seek time due to fragmentation (686ms vs 567ms, or a mere 1.2x difference).

Based on my experience I'm inclined to accept fuzzbang's description of block allocation strategies. It used to be common wisdom that you could defragment a volume by copying all the data off, formatting it, then copying the data back on. I did this once with an NTFS volume (using ntfs-3g), then checked the resulting data in the Windows disk defragmenter. The data was primarily located around the center of the volume, with numerous gaps. Filesystems leave gaps to allow room for files to expand.

B) You have just named three uncommon filesystems that few people will ever use in the first place, much less with TrueCrypt.

"Commonness" for the purposes of forensics is a much lower bar than for market analysis. I'd also wager that, servers included, there are at least as many ext2/ext3/ext4 volumes on the planet as NTFS volumes.

[nknighthb]

> If you haven't actually looked at the block allocation patterns of common filesystems

I have.

> you can't say conclusively that fuzzbang is incorrect

And I can.

I'm aware of the degree of difference in speed. It is sufficient that it is standard practice for filesystems to be restricted to the first 1/4-1/2 of a spinning disk in performance-sensitive applications. Or at least it was, in the last few years we've become more likely to just use SSDs or keep everything in RAM.

> if that 200MB file is stored in 100 2MB fragments

Thank you for assuming I don't even have the knowledge of a typical computer user, it greatly increases the likelihood I'll not waste further time with you. Raises it, in fact, to 100%.

[nitrogen]

> If you haven't actually looked at the block allocation patterns of common filesystems

I have.

And? What distribution of block allocation did you observe on said filesystems? Does it contradict the original supposition that filesystems spread out allocations to prevent fragmentation, thus possibly overwriting hidden data at the end of a partition?

It is sufficient that it is standard practice for filesystems to be restricted to the first 1/4-1/2 of a spinning disk in performance-sensitive applications.

This has as much to do with seek times as sequential reading speed. A drive with 8ms average seek times might average 2ms if you only make the heads travel 25% of the width of the platter.

The fact that you have to restrict the filesystem to the beginning of the disk suggests that filesystems don't do this automatically.

Thank you for assuming I don't even have the knowledge of a typical computer user, it greatly increases the likelihood I'll not waste further time with you. Raises it, in fact, to 100%.

I'm not sure how you got that impression. I was just providing numbers to complete the example. There's no need to become defensive; and if you find that you might be wrong, saying, "That's a fair point, I'll have to do some more research," goes a lot further than continuing to beat a dead horse.

Maybe it's the fact that this thread is on an article related to law, politics, and morality that is causing needless argumentation.

[schrodinger]

HFS+ is not exactly uncommon

[nknighthb]

As a full-time Mac user for 8 years, and a Linux user for much of the decade before that, I am acutely aware of how common many filesystems, including HFS+, actually are.

If OS X ever breaks 10% (and still uses HFS+ at that time), I'll reconsider my judgement of its commonality.

[davidcuddeback]

I'm writing this from a computer with two partitions: one HFS+ running OSX and one Ext4 running Linux. These are both the default options when installing OSX (Mountain Lion) and Ubuntu 12.04, respectively:

https://www.dropbox.com/s/x3cluigwaog8sad/gparted.png

[nknighthb]

Of course you are. And if you took a poll of HN users, you might even find OS X + Linux near a majority. That has nothing at all to do with what filesystems the vast majority of people are using, much less what they'd be using with TrueCrypt.

[schrodinger]

It's over 7%, I still wouldn't call that uncommon and say few people use it.

http://en.m.wikipedia.org/wiki/Usage_share_of_operating_syst...