From: Lauriault Yvon (yvon.lauriault@nlc-bnc.ca)
Date: Fri Mar 14 2003 - 14:48:08 EST
Thanks to all who responded.
Turns out the blocksize used to create the tape was 512 bytes. It was
suggested to increase it to 64K to improve the throughput.
Yvon
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-- From: Haesaerts, Corinne [Corinne.Haesaerts@hp.com] better ask what blocksize was used. Was it just TAR or did it involve DD ?? ---------------------------------------------------------------------------- -- From: Rick Kelly [rmk@toad.rmkhome.com] Whoever created that tape used a block size of 1. The normal default block size is 16k. Unfortunately you can't change it. ---------------------------------------------------------------------------- -- From: Alan Rollow - Dr. File System's Home for Wayward Inodes. [alan@desdra.cxo.cpqcorp.net] It is most likely the small block size (512 bytes per tape block). You can check by getting tar out of the way and reading the tape directly with dd(1): time dd if=tape-device-name of=/dev/null bs=1b If you use the no-rewind tape device, this will avoid timing the rewind. For a small archive this might add noticable time. If you want to limit the amount of data read to get your performance estimate, use the "count=" option on the dd(1) command. I think the only way to get this to read faster is to have the tape rewritten with a useful block size. tar defaults to 10 KB on most systems and that's not bad for a DLTtape III. With the a DLT III tape, the performance will limited to around 1.5 MB/sec, though it may peak higher with compression (PDF and TIFF may already be compressed so that won't help). DLT IV can go higher with a decently written tape and the right data stream. With the DLT IV tapes, the TZ89 like large block sizes. 256 KB isn't bad if you can coerce tar to write it. ---------------------------------------------------------------------------- -- From: Dr Thomas.Blinn@HP.com [tpb@doctor.zk3.dec.com] If the tape was truly created with a blocksize (blocking factor) of 1, then it has 512 byte records, and nothing you do on your system is going to speed up the data rate for reading it. You need to get the tape written with a higher blocking factor; at least 10, maybe more like 50, or even 64 if the Sun system can support 8K data writes to tape. ---------------------------------------------------------------------------- -- From: Alan Rollow - Dr. File System's Home for Wayward Inodes. [alan@desdra.cxo.cpqcorp.net] Just as an extra bit of information... I used dd(1) to write a copy of /vmunix (9,141,408 bytes) to my TZ87. With a DLT III the performance will be comparible to the TZ89 using the same kind of tape. Writing at 1 sectors per tape block took 91 seconds: 98 KB/sec Writing at 128 sectors per tape block took 7 seconds: 1275 KB/sec Reading of each: 512 bytes -> 122 KB/sec 64 Kbytes -> 2231 KB/sec The performance you saw is to be expected. Take comfort in the fact that it probably took the other side longer to write it. ---------------------------------------------------------------------------- -- -----Original Message----- I have received a DLT III tape (density 10/15) that was created using TAR on a SUN server and find that it is very slow to read (120 KB/sec) using a TZ89 (35/70) drive connected to a GS140 Tru64 v5.1 pk5. The data on that tape is TIFF images imbedded in PDF files with an average of 4MB each. I noticed that when I started TAR it displayed "blocksize = 1". Is 120 KB/sec normal with this setup? If not, any suggestions to improve the throughput? Blocksize maybe? What value? Thanks in advance. yvon.lauriault@nlc-bnc.ca <mailto:yvon.lauriault@nlc-bnc.ca>
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