TAPEBLK and LTAPEBLK
I am looking for some advice on how to tune TAPEBLK and LTAPEBLK when using disk devices for TAPEDEV and LTAPEDEV. Is there any reason to move away from the default of 32KB and match the values to the block size of my filesystem, i.e. 8KB?
Desmodromic wrote: > I am looking for some advice on how to tune TAPEBLK and LTAPEBLK when > using disk devices for TAPEDEV and LTAPEDEV. Is there any reason to > move away from the default of 32KB and match the values to the block > size of my filesystem, i.e. 8KB? No - but there might be grounds for going to, say, 256 KB in order to get the tape drives to stream properly. If you're actually writing to disk, the difference is immaterial; if you're really using tape devices, the block size can be significant. Once upon a long, long time ago, I learned that the hard way. I wrote a tape (9-track half-inch - the old classic drives from the movies) with 1/2 KB blocks on a drive that did buffering and wrote them fairly continuously. When it came to reading the tape on a less intelligent device, it took forever to read the tape, watching it rock forwards to read a 1/2 KB block, then rock back, and then rock forward for the next one. Block size (sometimes) matters - be sure you know whether it does. -- Jonathan Leffler #include <disclaimer.h> Email: jleffler@earthlink.net, jleffler@us.ibm.com Guardian of DBD::Informix v2005.02 -- http://dbi.perl.org/
Use dd to write to a tape any use increasing bs= until you get to one that doesn't work, then use the last good one! On a SCSI connected drive this could be as high as 16MB but on an AIX Fibre connected drive I've found 1MB was as high as I could go. Keith On 26/10/06, Jonathan Leffler <jleffler@earthlink.net> wrote: > Desmodromic wrote: > > I am looking for some advice on how to tune TAPEBLK and LTAPEBLK when > > using disk devices for TAPEDEV and LTAPEDEV. Is there any reason to > > move away from the default of 32KB and match the values to the block > > size of my filesystem, i.e. 8KB? > > No - but there might be grounds for going to, say, 256 KB in order to > get the tape drives to stream properly. If you're actually writing to > disk, the difference is immaterial; if you're really using tape devices, > the block size can be significant. > > Once upon a long, long time ago, I learned that the hard way. I wrote a > tape (9-track half-inch - the old classic drives from the movies) with > 1/2 KB blocks on a drive that did buffering and wrote them fairly > continuously. When it came to reading the tape on a less intelligent > device, it took forever to read the tape, watching it rock forwards to > read a 1/2 KB block, then rock back, and then rock forward for the next one. > > Block size (sometimes) matters - be sure you know whether it does. > > -- > Jonathan Leffler #include <disclaimer.h> > Email: jleffler@earthlink.net, jleffler@us.ibm.com > Guardian of DBD::Informix v2005.02 -- http://dbi.perl.org/ > _______________________________________________ > Informix-list mailing list > Informix-list@iiug.org > http://www.iiug.org/mailman/listinfo/informix-list >
I tend to set it at 1024, works fine for me. A very unscientific way (depending on tape device) is to increase until the tape write light is on permanently Paul Watson Tel: +44 1414161772 Mob: +44 7818003457 Web: www.oninit.com GO FURTHER with DB2 GET THERE FASTER with Informix. Attend IDUG 2007 San Jose, North America May 6-10, 2006 Visit http://www.iiug.org/conf for more information. > -----Original Message----- > From: Desmodromic [mailto:davies_ms@yahoo.com.au] > Posted At: 25 October 2006 22:08 > Posted To: comp.databases.informix > Conversation: TAPEBLK and LTAPEBLK > Subject: TAPEBLK and LTAPEBLK > > > I am looking for some advice on how to tune TAPEBLK and > LTAPEBLK when using disk devices for TAPEDEV and LTAPEDEV. Is > there any reason to move away from the default of 32KB and > match the values to the block size of my filesystem, i.e. 8KB? >
most of the advice works provided that the tape drive you are writing to is the same as the one you will be reading from However as jon said you need to consider the effectiveness of the block size of the tape drives on both the source and target systems. This will often be the same device.