[zfs-discuss] ZFS eating up all 16 GB RAM when combining 4k blocksize ZVOL with XFS

Omar Siam simar at gmx.net
Tue Nov 13 13:50:01 EST 2018


Hi Edward!
> What  brings you to that conclusion? I didn't see anything in your post that really suggested any one explanation at all... Except generically, something consumed all the memory...

I am looking for a way to prove that or find whatever other cause there 
may be.
First: That something is hidden. No easily accessible kernel or user 
space stat shows it. So of course I can't point to what consumes all the 
RAM.
Second: This happens only when writing using explicitly libaio. Data is 
written before that and there isn't anything remarkable. If I use 
LIO/iSCSI from another machine with the same programs and XFS filesystem 
it works. If I use SCST the target machine with the ZVOL crashes at the 
same point, the second attempt to write to a file using 2MB chunks using 
libaio. Of course that may be unrelated but it looks very suspicious.
Third: It also works with another ZFS implementation but the same 
hardware and virtualization of the same minimal Ubuntu 18.04.1 
installation on freenas. That makes it very unlikely in my opinion that 
the problem is somewhere else in the Linux kernel.

So if you have any suggestions what test I could run to make sure it 
isn't about Linux asynchronous writes and ZFS ZVOL please tell me.

Best regards
Omar



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