[zfs-discuss] General Questions on ARC & L2ARC

Pandu Poluan pandu at poluan.info
Thu Aug 29 00:57:25 EDT 2013


Hello, people!

I'm quite new to ZFS, but even then already love it to death -- had some 
brushes with disaster that were averted by a timely 'zfs rollback', and now 
my boss loves ZFS, too :-)

I hope I don't come across as an annoying newb, but I have several 
questions around ARC & L2ARC.

1. Since ZFS' ARC might fell victim to Linux memory fragmentation [1], 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 issue as the 
zfs module can allocate the ARC memory since boot?

2. I have also read several times in this forum/group about employing ZRAM 
for L2ARC. On benefit mentioned in [1] is that L2ARC size is constant, so 
it will not cause 'gotchas' like what happens when ARC baloons in size. But 
I've searched and yet to find a comprehensive analysis on this strategy's 
benefits vs drawbacks. Can someone point me to such resource and/or provide 
me with one?

Thank you very much for your assistance.


[1] "ZFS consuming twice ARC's size and crashing system" 
https://groups.google.com/a/zfsonlinux.org/d/topic/zfs-discuss/wlS8GqjixJk/discussion


Rgds,
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