[mythtv-users] Poor performance with ZFS (ZFS on Linux)

[Mark Wedel]

  I'm running zfs on linux with mythtv, and haven't noticed issues.  But I'm 
also not doing strict timing comparisons.  Is the 2 minutes to run 
mythfilldatabase causing problems, or are you just comparing it ext4?  Different 
filesystems can do different things better - it would not surprise me in some 
cases that zfs performs worse than ext4, but zfs has lots of features that make 
it useful, so may be willing to take the performance hit.

  Looking at my system, it appears it takes about 15 seconds for 
mythfilldatabase to run.  But this could also vary based on how much data is 
being fed in.

  Likewise, a dump of the entire database (mysqldump -p mythconverg > /dev/null) 
takes less than 2 seconds, though that may be mostly because everything is in 
memory.  I can't remember for sure, but I think the my.cnf I'm using is based on 
a large config - system has 32 GB of ram, so I can afford to give mariadb some 
memory to run with.  System also runs zoneminder, so I apparently added these to 
the my.cnf at some point:

#
# Suggestion for zoneminder
#
innodb_file_per_table
innodb_log_file_size=512M

  My root filesystem is on ssd.  I did not bother to make a separate dataset 
with a non default recordsize - it is using the 128k.

  RE compression/non compression - I was once told that using compression is 
almost always a win, because current systems have so much cpu power that the 
time to compress the data is trivial, and the fact that you are saving on I/O 
operations means you have a net gain.  This may be less true for SSD, where I/O 
is pretty fast (and may be even less so for NVME).  But if you are still using 
HDD, you probably come out ahead, depending on what you store (the actual 
recordings are already compressed, so my compress ratio on those is only 1.06, 
so not really much.