On Wed, Oct 15, 2014 at 05:26:52PM +0200, you (Jakob Borg via smartos-discuss) sent the following to [smartos-discuss] : > So I noticed the fairly recent addition of the FRAG column in pool output. > > [root@anto ~]# zpool list > NAME SIZE ALLOC FREE EXPANDSZ FRAG CAP DEDUP HEALTH ALTROOT > data 16.3T 4.67T 11.6T - 0% 28% 1.00x ONLINE - > zones 1.06T 245G 843G - 34% 22% 1.00x ONLINE - > > This ought to be a measure of pool fragmentation. 0% on the "data" > pool makes sense; the data here is essentially static, write-once > read-many data. The "zones" pool is seeing slowly increasing > fragmentation. I'm guessing this will reach a steady state at some > level, based on for example the writeup of fragmentation in > http://blog.delphix.com/uday/2013/02/19/78/. So the things I wonder > are: > > What does the percentage mean exactly (number of what per what?) and > where might I expect it to stabilize for a 22% full pool? > > The Delphix blog post shows a fairly drastic decrease in write > performance with increased fragmentation. This sounds bad, and I guess > it's this effect that motivates showing the percentage in the first > place. But I don't really get why that is, while the pool is still > fairly empty? The number of free blocks is the same, they just aren't > contiguous. Is the issue with large sequential writes that then cannot > be sequential? In that case it would be mostly a nonissue for the > "zones" pool that usually sees small, random, sync writes (KVM etc)? >
Thanks for this. I've been meaning to raise this question myself but forgot about it. -- Marco van Lienen -- Unix Systems Engineer -- http://lordsith.net/ GnuPG id: 8580E6CB You can have it in any color you want as long as it is black! ------------------------------------------- smartos-discuss Archives: https://www.listbox.com/member/archive/184463/=now RSS Feed: https://www.listbox.com/member/archive/rss/184463/25769125-55cfbc00 Modify Your Subscription: https://www.listbox.com/member/?member_id=25769125&id_secret=25769125-7688e9fb Powered by Listbox: http://www.listbox.com
