tar, mt backup BLOCKSIZES, variable fixed question Seagate SDT224000N DDS-3 DAT
Hello, I'm having trouble understanding the tar mt blocksize settings and operation. From information around the internet, I think this is how it works but I want to run it by someone else who really knows: If I run mt blocksize 1024, that sets the actual drive to write data in 1024 byte blocks. If I make an archive with tar with flag -b 20, tar will format and send 10,240 byte blocks to the tape drive and the tape drive will then subdivide those into 1024 byte blocks and put them onto the tape. Working with larger blocksizes in tar better insures that the drive is always getting data, thereby making it not need to ever rewind to catch up if there is a delay in the host computer's data access. However, I am getting inconsistent information on the variable blocksize setting in mt and don't know if I should use it or not. One site I found said that variable blocksizes allow the drive to write blocks at a size that it thinks will be best for the data speed at hand, while another site said that it allows the drive to use the blocksize being sent to it from the backup application (making 10,240 byte blocks in the above tar example). Who is right, or have I got this all mess up? :) Also is there a preferred blocksize for DDS-3 DAT drives? Thank You Kindly, Jonathan I'm using a Seagate SDT224000N DDS-3 DAT drive on FreeBSD 5.1-RELEASE. ___ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: tar, mt backup BLOCKSIZES, variable fixed question Seagate SDT224000N DDS-3 DAT
In the last episode (Dec 12), Jonathan Wright said: up if there is a delay in the host computer's data access. However, I am getting inconsistent information on the variable blocksize setting in mt and don't know if I should use it or not. One site I found said that variable blocksizes allow the drive to write blocks at a size that it thinks will be best for the data speed at hand, while another site said that it allows the drive to use the blocksize being sent to it from the backup application (making 10,240 byte blocks in the above tar example). Who is right, or have I got this all mess up? :) variable blocksize means write data to tape using whatever size chunks the user write()s. I think only ancient QIC tapes actually need you to set a fixed blocksize via mt. Also is there a preferred blocksize for DDS-3 DAT drives? I use 64k for everything. -- Dan Nelson [EMAIL PROTECTED] ___ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: tar, mt backup BLOCKSIZES, variable fixed question Seagate SDT224000N DDS-3 DAT
If I run mt blocksize 1024, that sets the actual drive to write data in 1024 byte blocks. If I make an archive with tar with flag -b 20, tar will format and send 10,240 byte blocks to the tape drive and the tape drive will then subdivide those into 1024 byte blocks and put them onto the According to the tar manual, you should use a blocking factor that suits the average file size in the archive. It also says that tape and cartridge media likes larger blocking factors, as it will give better throughput and minimize tape and head wear. I use 128 with my DDS2 drive. Also, 20 is the default, so if that's what you want to use you don't need to specify it. Have a look here for more info: http://www.gnu.org/software/tar/manual/html_node/tar_132.html ___ [EMAIL PROTECTED] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to [EMAIL PROTECTED]
