[zfs-discuss] General Questions on ARC & L2ARC

Sander Smeenk ssmeenk at freshdot.net
Thu Aug 29 05:50:26 EDT 2013

Quoting Uncle Stoatwarbler (stoatwblr at gmail.com):

> >what if I just set zfs_arc_min = zfs_arc_max ? Won't that cause the ARC
> >to stay at a fixed size, hence not affected by memory fragmentation
> It should work.

It should. But probably won't. At least, that's my experience with
tweaking the zfs_arc_m{in,ax} settings. It did not seem to have any
effect other than changes in the Munin graphs for my ZFS-setup. ;)

> I do something similar on my own system (min = 0.75*max) and I've
> never seen the complained about behaviour, however I also set
> metadata_max = 0.8 * arc_max.

I haven't played with metadata_max.

> >2. I have also read several times in this forum/group about employing
> >   ZRAM for L2ARC.
> The latest compressed l2arc in 0.6.2 means you don't really need it
> anymore.

True. You don't need *Z*RAM anymore.
However i do have the feeling that adding ${physcpucores} of L2ARC cache
devs to your pool DOES make the system more stable, fragmentation wise.

With 0.6.2 you could use just plain ramdisk blockdevices. (/dev/ramN)

Please go with ZoL v0.6.2. It seems much more stable.

My 25ct,
| 42.7 percent of all statistics are made up on the spot.
| 4096R/20CC6CD2 - 6D40 1A20 B9AA 87D4 84C7  FBD6 F3A9 9442 20CC 6CD2

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