Date: Tue, 26 Aug 2014 13:33:42 -0400 From: Daniel Staal <DStaal@usa.net> To: freebsd-questions@freebsd.org Subject: Re: some ZFS questions Message-ID: <C0A451924D1D1C5649C27787@[192.168.1.50]> In-Reply-To: <201408260651.s7Q6pijc023521@sdf.org> References: <201408070816.s778G9ug015988@sdf.org> <27DAA821-0303-4D51-ADA7-7780DB8FE85D@kraus-haus.org> <201408210837.s7L8bm01019230@sdf.org> <9207FB2C-5EDE-49A7-9B0E-7C9839250A7E@kraus-haus.org> <201408241001.s7OA19dZ004925@sdf.org> <5C83C4FD-571B-4557-8AD7-5578276D2ED5@kraus-haus.org> <201408260651.s7Q6pijc023521@sdf.org>
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--As of August 26, 2014 1:51:44 AM -0500, Scott Bennett is alleged to have said: > Paul Kraus <paul@kraus-haus.org> wrote: > >> On Aug 24, 2014, at 6:01, Scott Bennett <bennett@sdf.org> wrote: >> >> > Paul Kraus <paul@kraus-haus.org> wrote: >> >> >> I tend to agree. I do not recall off the top of my head, but I >> >> *think* you can enable compression on a zvol, in which case you can >> >> get that added benefit on the encrypted data, if you have the CPU >> >> power to handle both the encryption and the compression at once >> >> without too big a performance penalty. >> > >> > That may be worth keeping in mind for the future, but my present >> > collection of both encrypted and unencrypted file systems that are >> > candidates to be moved into the care of ZFS are almost entirely >> > compressed already. Turning on compression for these would just add >> > unnecessary CPU overhead. >> > Hmm...how would zvol compression work? Would UFS2 data structures >> > still be meaningful? Would geli(8) or other g* utilities be able to >> > find the last sector(s) in order to create/read their label metadata? >> >> OK, I just checked and my zvol *does* have a compression property, so >> you can enable compression for zvols. > > That's good to know in case I someday have other archival needs, but > in the current situation, wouldn't buy me much, if anything, for the CPU > costs, as noted above. --As for the rest, it is mine. Compression can be well worth the CPU cost, actually: In many cases using light/medium compression under ZFS *improves* performance, as it takes less time to compress/decompress the data then it does to transfer the uncompressed data to disk. Experiment with your data, of course; it depends on how compressible things are, and your hardware. But don't write it off just because it's a CPU cost - it might still be a good option. Daniel T. Staal --------------------------------------------------------------- This email copyright the author. Unless otherwise noted, you are expressly allowed to retransmit, quote, or otherwise use the contents for non-commercial purposes. This copyright will expire 5 years after the author's death, or in 30 years, whichever is longer, unless such a period is in excess of local copyright law. ---------------------------------------------------------------
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