On 2012-08-21 05:42, Alan Brown wrote: > On 21/08/12 08:37, lst_ho...@kwsoft.de wrote: >> Some short tests with the "Maximum Block Size" set, show transfer >> speed to the LTO-4 of 87MBytes/sec with 256K and 98MBytes/sec with >> 1M >> with Bacula encrypted data, so with this we are reaching the >> theoretical uncompressed speed of the LTO-4 device by ~20%. It would >> be really helpful if there is some developer to say if there is any >> downside of large block sizes? > > I'm not a dev, however I use 2Mb block size (this is the largest > bacula > currently supports)
I suspect I'm an edge case with tape. I'm using old technology and old hardware. That's what I can afford on a home network. I wasn't sure what block size I'm using on my DLT-7000 tape library, but I see it's variable.... $ sudo mt -f /dev/nsa0 status Mode Density Blocksize bpi Compression Current: 0x1b:DLTapeIV(35GB) variable 85937 IDRC ---------available modes--------- 0: 0x1b:DLTapeIV(35GB) variable 85937 IDRC 1: 0x1b:DLTapeIV(35GB) variable 85937 IDRC 2: 0x1b:DLTapeIV(35GB) variable 85937 IDRC 3: 0x1b:DLTapeIV(35GB) variable 85937 IDRC --------------------------------- Current Driver State: at rest. --------------------------------- File Number: 0 Record Number: 0 Residual Count 0 All my tape jobs involve data on local HDD. That is, I backup to disk first, then copy to tape. The HDD and the tape are both connected to the same bacula-sd. > The only downside is that you _must_ mark all active tapes as "used" > before changing block size. Setting them as USED is fine by me. I write my tapes until they are FULL. Checking the recycling algorithm documentation[1], this will not affect pruning. > Bacula will be able to read the old tapes, but it cannot handle > maximum > block size changing midway through a tape. I found one reference[2] after a bunch of searching, but I should look more: ### The DLT drive default data block transfer size is 4KB (4096 bytes). To achieve better performance, adjust block size to 32K bytes or higher when using a fixed block device. ### My full backups, roughly 90GB, take about 12 hours to copy to tape. Thus, my only incentive to change blocksize is to avoid shoe-shine, which I do not think is happening at present. [1] - http://www.bacula.org/5.2.x-manuals/en/main/main/Automatic_Volume_Recycling.html [2] - http://techpubs.sgi.com/library/dynaweb_docs/hdwr/SGI_Admin/books/DLT_OG/sgi_html/ch05.html -- Dan Langille - http://langille.org/ -- Dan Langille - http://langille.org/ ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Bacula-users mailing list Bacula-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bacula-users
