[lustre-discuss] Relaxing read consistency, from other node write

[Hans Henrik Happe]

Hi,

Some users experienced that reading a log file written on another node 
the read of the last bytes were sometimes delayed teens of seconds. This 
happens when other processes are writing heavily.

It seems that the data needs to be committed to persistent storage, 
before the reading node can have it. That makes sense since the writing 
node and the server could die, taking with them all knowledge about the 
write. Is this a correct description?

I'm wondering if there is a way to relax this. I.e. ignore this failure 
scenario or treat the cache entries in writing node and server as enough 
redundancy?

WRT why we see these long delays I think I tracked it down to an ZFS 
issue (https://github.com/zfsonlinux/zfs/issues/4603), but I'm only a 
layman when it comes to the internals of ZFS and Lustre.

We are at 2.7.64, so we have to update to 2.8 soon. Going through the 
commits I couldn't find anything that relates, but that might just be my 
ignorance.

Cheers,
Hans Henrik