Date: Wed, 12 Oct 2011 08:59:29 +0100 From: "Steven Hartland" <killing@multiplay.co.uk> To: "Dennis Glatting" <freebsd@penx.com>, <freebsd-fs@freebsd.org> Subject: Re: ZFS/compression/performance Message-ID: <740CDE42E82044428B5FAA3FC73ABD32@multiplay.co.uk> References: <alpine.BSF.2.00.1110111710210.12895@Elmer.dco.penx.com>
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----- Original Message -----
From: "Dennis Glatting" <freebsd@penx.com>
>I would appreciate someone knowledgeable in ZFS point me in the right
> direction.
>
> I have several ZFS arrays, some using gzip for compression. The compressed
> arrays hold very large text documents (10MB->20TB) and are highly
> compressible. Reading the files from a compressed data sets is fast with
> little load. However, writing to the compressed data sets incurs
> substantial load on the order of a load average from 12 to 20.
>
> My questions are:
>
> 1) Why such a heavy load on writing?
> 2) What kind of limiters can I put into effect to reduce load
> without impacting compressibilty? For example, is there some
> variable to controls the number of parallel compression
> operations?
>
> I have a number of different systems. Memory is 24GB on each of the two
> large data systems, SSD (Revo) for cache, and a SATA II ZIL. One system is
> a 6 core i7 @ 3.33 GHz and the other 4 core ii7 @ 2.93 GHz. The arrays are
> RAIDz using cheap 2TB disks.
Have you tried using the alternative compression algorithms
e.g. lzjb or gzip-[1-5] the default gzip = gzip-6
Regards
Steve
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