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)? //jb ------------------------------------------- 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
