On Tue, 3 Aug 2021, Linus Torvalds wrote: > On Tue, Aug 3, 2021 at 5:04 PM Theodore Ts'o <tytso@xxxxxxx> wrote: > > > > Whenver I've ever needed to access ntfs files, I've always used the > > ntfs-3g FUSE package. > > The user-space FUSE thing does indeed work reasonably well. > > It performs horribly badly if you care about things like that, though. > > In fact, your own numbers kind of show that: > > ntfs/default: 670 tests, 55 failures, 211 skipped, 34783 seconds > ntfs3/default: 664 tests, 67 failures, 206 skipped, 8106 seconds > > and that's kind of the point of ntfs3. In all fairness, the generic/405 test case completely distorted the overall timing in favour of ntfs3. Neither driver was involved in that test case. Generic/405 test is mkfs against a 1 TB thin provision device which has 1 MB backing size. mkfs should return an error after it hits EIO. The test case configuration was not correct for mkntfs on behalf of ntfs-3g because it missed the --fast format option, so mkntfs tried to fill the 1 TB device with zeros, apparently on Google Cloud Platform, for almost 8 hours. This had absolutely nothing to do with ntfs-3g performance, it was a pure mkfs test: https://github.com/kdave/xfstests/blob/master/tests/generic/405 Meanwhile the test case ran in 1 second on behalf of ntfs3 because its mkfs was not found, so the test could not be run. (And the test case got incorrectly categorized as success because it interpreted the "command not found" error as a success.) If this mkntfs test case is ignored, as it should be, then ntfs-3g's runtime was (34783 - 28396) = 6387 versus ntfs3's (8106 - 1) = 8105 seconds, i.e. the user space ntfs-3g was about 21% faster overall than the kernel space ntfs3. Does this mean ntfs-3g is faster than ntfs3? Of course not. Fstests is not a benchmark. What we know for sure is, the unknowingly configured, untuned versions of the software gave different times for different workloads. File system performance is a fairly complex topic. Ntfs-3g always aimed for stability, features, interoperability and portability, not for best possible performance. There seems to be some misconceptions, misinterpretations, inefficient configuration and mount options (e.g. missing big_writes, kernel_cache, etc). Unfortunately we did our part too to end up here. We will set better performance defaults in future releases. User space drivers can have major disadvantages for certain workloads however how relevant are those for NTFS users? Most people use NTFS for file transfers in which case ntfs-3g read and write speed is about 15-20% less compared to ext4. For example in some quick tests ext4 read was 3.4 GB/s versus ntfs-3g 2.8 GB/s, and write was 1.3 GB/s versus 1.1 GB/s. Additionally there are still several technical solutions which could be implemented to improve all kinds of user space driver performance significantly. But again, we always prefer data integrity over performance. And NTFS can be quite tricky with the ever changing on-disk corner cases. Does anybody still remember when Windows 2000 changed the NTFS on-disk format which massively started to trash users' data? Please don't get me wrong, I'm not saying this is the way to go (who would be so crazy to write anything like that on the linux-kernel list?) I'm just saying this is the way we chose and support. We welcome the recent interest in NTFS after working on it for 20 years. ------ These are from Ted's logs which he shared earlier. It's much appreciated, it was highly useful. Personally I also thought the very poor ntfs-3g timing was due to bad configuration and/or mount options instead of an irrelevant test case. (Btw, the driver configuration and mount options were indeed not right, e.g. ACL, permission, etc related cases failed which could have pass.) $ egrep ^generic/405 results-ntfs*/runtests.log results-ntfs/runtests.log:generic/405 [21:47:08] [05:40:24] 28396s results-ntfs3/runtests.log:generic/405 [12:12:09] [12:12:10] 1s $ cat results-ntfs/ntfs/results-default/generic/405.full [...] Cluster size has been automatically set to 4096 bytes. Initializing device with zeroes: 100% - Done. Creating NTFS volume structures. Failed to sync device /dev/mapper/thin-vol: Input/output error Syncing device. FAILED $ cat results-ntfs3/ntfs3/results-default/generic/405.full [...] mkfs: failed to execute mkfs.ntfs3: No such file or directory Best regards, Szaka
