Date: Mon, 30 May 2005 13:26:46 -0300 From: =?ISO-8859-1?Q?Tulio_Guimar=E3es_da_Silva?= <tuliogs@pgt.mpt.gov.br> To: freebsd-hardware@freebsd.org Subject: Re: Weird behaviour of AIT-3 and (g)tar Message-ID: <429B3EC6.7000905@pgt.mpt.gov.br> In-Reply-To: <428DFF35.1000409@pgt.mpt.gov.br> References: <428CF20F.50607@pgt.mpt.gov.br> <428D0D79.7010506@rcn.com> <428DFF35.1000409@pgt.mpt.gov.br>
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Up and again, a little more testing showed that "compression enabled" is slower and fits *less* data than having it disabled. I dumbly didnīt save the screen results, but I can repeat the tests and post the exact messages, if needed. For now, what I can say is compression dropped the transfers from about 11,8 MB/s to 10MB/s and reduced the capacity from about 95GB to 85GB. I repeated 2 times each test, with little variation, and maintained block sizes of 64kb, filtering with dd: To store: # dd if=/home/bkp/backup_050425.tar of=/dev/esa0 bs=64k To restore: # tar -b 128 -xvOf /dev/esa0 | dd of=/dev/null Note: I donīt know if the tape rewinding+ejection time counted in the total time. I used /dev/null to be sure HD performance would not interfere. In fact, writing to the tape was about 1% slower than reading. Would this be expectable? Tulio Tulio Guimarães da Silva wrote: > Hi Gary, > ouch! Thatīs quite disappointing... :( We had already noticed this > kind of behaviour with DDS-* tapes, but we got some progress varying > the block size... and yup, Iīm really using gzipped data. :S > For AIT-3, however, i thought this hardware compression was something > about using lower tapeīs phisical-rolling speeds or alikes, but I > could never really find anything concrete about the methods... the > only one thing I found was they could use "variable block sizes", but > thatīs all. Again, not many details. Anyway, Iīm giving up the idea of > compression for now. > If something, Iīm noticeing that (at least with -b 10) it becomes (a > lot) slower with time, but I guess this would be more of a question to > the -performance list. > Add: while writing this message, I remembered to check the 700Vīs > "Product Specification Manual", and they mention something about > dual-partitions, but it seems something that needs to be implemented > at driver level, since it includes SCSI commands. In this case, I > would need to format the tape as a 2-partition one... any clue about > if and/or how that works on FreeBSD? > Thanks again, > > Tulio > > Gary Corcoran wrote: > >> Tulio Guimarães da Silva wrote: >> >>> Hello again, >>> >>> Iīm having some trouble putting a Sony SDX-700V SCSI AIT-3 unit >>> to work on FreeBSD 5.3-RELEASE. >> >> >> ... >> >>> Besides the speed, hardware compression seems to not being >>> funcional either. I already tried every 4 possible dip switch >>> setting for compression, but I am still not able to transfer a 180GB >>> archive to a (should-be) 260GB medium. >> >> >> >> I can't help you with most of your problems, but regarding the >> "compression"... >> >> I would guess that if you have 180GB to backup, it's not all text. :) >> When I last used a tape drive years ago, when writing to a 2GB tape >> that would supposedly hold 4GB compressed, I could fit only about 1.9GB >> before the tape was full. Turning off hardware compression, I could fit >> 2GB. The problem was that I was saving already compressed multimedia >> files, >> and the tape drive's "compression" just added overhead and took up >> more space. >> So unless you're backing up text or similar files, don't believe the >> marketing hype about getting 2x the amount onto your tapes... >> >> Gary > > >------------------------------------------------------------------------ > >_______________________________________________ >freebsd-hardware@freebsd.org mailing list >http://lists.freebsd.org/mailman/listinfo/freebsd-hardware >To unsubscribe, send any mail to "freebsd-hardware-unsubscribe@freebsd.org" > >
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