XFS fragmentation performance impact (Unraid/Plex)

[tikker]

Recently my Plex server has started acting weird: Some 4k HDR HEVC files with TrueHD streams simply refuse to play 99% of the time and if they do any 'seeking trigger' like resume, fast-forward, rewind or toggling subtitles will result in a stuck loading screen which will eventually result in "Unable to playback media" and a

DEBUG - Failed to stream media, client probably disconnected after X bytes: 104 - Connection reset by peer

in the logs.

 

The server runs Unraid 6.8..3 and I have now localised it to apparently a specific disk in the array. A small sample test seems to confirm that. Movies on other disks play fine, but the tested ones that reside on the disk in question show the same stuck-loading behaviour. Switching to a lower-bandwidth audio stream in the file immediately fixes it however and switching back to high-res audio breaks it again and triggers a warning about the connection to the server not being fast enough. The latter I doubt, as it is connected over gigabit.

 

Now the one thing that makes this disk stand out is that it is highly fragmented compared to the rest:

root@<server>:~# xfs_db -r -c frag <disk>
actual 2288, ideal 1336, fragmentation factor 41.61%
Note, this number is largely meaningless.
Files on this filesystem average 1.71 extents per file

all the other disks are between 5 and 10%.

 

I'm not that intimately familiar with file systems other than NTFS, so my question is: can/will such a high fragmentation cause these kind of issues and should I maybe put a defrag in a cron job or something to once in a while defrag stuff?

[tikker]

Well I let it run over the day and can confirm that it didn't help. Debugging continues... In hindsight as well, fragmentation is fragmentation and I just misinterpreted the hearsay of these filesystems being more resistant against fragmentation to think that fragmentation would be more of a bad thing for them.

[Jarsky]

I dont think it would be a disk issue. If its working when you switch the transcoder to a lower quality that seems more Plex specific. 

Consider the file still needs to be read in its original bitrate in order to transcode it. So if the disk can keep up for transcoding, its the same as Direct Stream as far as the drive is concerned. 

 

[tikker]

1 hour ago, Jarsky said:

I dont think it would be a disk issue. If its working when you switch the transcoder to a lower quality that seems more Plex specific. 

Consider the file still needs to be read in its original bitrate in order to transcode it. So if the disk can keep up for transcoding, its the same as Direct Stream as far as the drive is concerned. 

 

Yeah it could well be a Plex issue. It's not hard to find complaints about HEVC content not behaving well on it with a variety of circumstance. Note that nothing is (or should be at least) transcoding. My equipment is capable of Direct Playing all my content. The weird thing is that it's specifically TrueHD streams on that disk. The same type of files (i.e. HEVC 4k HDR TrueHD) on other disks play just fine, DTS-HD MA files on the weird disk play just fine and any other lower bitrate audio also plays just fine.

 

Anything I could check on the drive? SMART status doesn't report anything unusual and it's the same drive as the rest of the array (WD Red 4 TB). I'll try moving one of the offending files to another disk to see if it still acts up or not. Last resort would be nuking the database and let it rebuild from scratch, but I'd rather avoid that if possible.

[tikker]

I guess it's just Plex. Kodi happily Direct Plays the content and even the Plex for Kodi plugin works completely fine with Plex reporting Direct Play... It's just Plex itself that refuses to play these files. Shame

[Jarsky]

3 hours ago, tikker said:

I guess it's just Plex. Kodi happily Direct Plays the content and even the Plex for Kodi plugin works completely fine with Plex reporting Direct Play... It's just Plex itself that refuses to play these files. Shame

 

Are we talking about Plex Web? 

I used to constantly have issues, and I still do have long delays with playback starting on some files. I find the Plex App in Windows typically works better. 

 

If you arent fully committed to Plex, I also find Emby just overall performs better and is more responsive. I also like how it doesnt interrupt playback when you enable / switch Subtitles in Emby which is a huge annoyance to me in Plex. 

[tikker]

9 hours ago, Jarsky said:

 

Are we talking about Plex Web? 

I used to constantly have issues, and I still do have long delays with playback starting on some files. I find the Plex App in Windows typically works better. 

 

If you arent fully committed to Plex, I also find Emby just overall performs better and is more responsive. I also like how it doesnt interrupt playback when you enable / switch Subtitles in Emby which is a huge annoyance to me in Plex. 

Nah the client on an Nvidia Shield connected to an AVR and OLED TV. I've tried all of Emby, Jellyfin, Kodi, Plex and despite them all having their faults I do prefer Plex for look and feel in the end.

 

It took a bit of digging, but in the end it did indeed turn out to be Plex. They updated their demuxer which apparently broke a bunch of things for many people. Installing the beta app that had a supposed fix resolved it.