Edward Ned Harvey (opensolarisisdeadlongliveopensolaris) wrote:
From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
boun...@opensolaris.org] On Behalf Of Jim Klimov
I really hope someone better versed in compression - like Saso -
would chime in to say whether gzip-9 vs. lzjb (or lz4) sucks in
terms of read-speeds from the pools. My HDD-based assumption is
in general that the less data you read (or write) on platters -
the better, and the spare CPU cycles can usually take the hit.
Oh, I can definitely field that one -
The lzjb compression (default compression as long as you just turn compression on without
specifying any other detail) is very fast compression, similar to lzo. It generally has
no noticeable CPU overhead, but it saves you a lot of time and space for highly
repetitive things like text files (source code) and sparse zero-filled files and stuff
like that. I personally always enable this. "compresson=on"
zlib (gzip) is more powerful, but *way* slower. Even the fastest level gzip-1
uses enough CPU cycles that you probably will be CPU limited rather than IO
I haven't seen that for a long time. When gzip compression was first
introduced, it would cause writes on a Thumper to be CPU bound. It was
all but unusable on that machine. Today with better threading, I barely
notice the overhead on the same box.
There are very few situations where this option is better than the default lzjb.
That part I do agree with!
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