On Thu, Aug 11, 2016 at 02:47:10AM +1000, Craig Sanders via luv-main wrote:
On Mon, Aug 08, 2016 at 02:05:47PM -0400, Robin Humble wrote:
I've 8G ram which should be heaps. limiting l2arc to 1G didn't help either. l2arc or arc? if l2arc, 1G isn't really worth bothering with and may even hurt performance.
<looks through command history> echo "options zfs zfs_arc_max=$((2*1024*1024*1024))" > /etc/modprobe.d/zfs.conf
on my intel SSD, ZFS is noticably slower than ext4. part of it's because of ZFS's poor integration with linux's virtual memory system and both sets of caches clearly fighting each other, have you tried setting zfs_arc_min = zfs_arc_max? that should stop ARC from releasing memory for linux buffers to use.
is that what most folks do? as the SSD is fast at large reads (500MB/s), I could also just cache metadata and not data. would that make sense do you think?
The most likely cause is that ext4 has excellent SSD TRIM support but ZFS on linux doesn't. There's a patch that's (finally!) going to be merged "soon": https://github.com/zfsonlinux/zfs/pull/3656
neat! cheers, robin