Ontape parameters

Dear colleagues: I need to make backups on tape. I have an external HP LTO Ultrium 6 drive with native 2.50TB cartridges, and my problem is focused on the TAPEBLK parameter, which I had at 2048 when I backed up to disk, but when I want to do it to tape, the ontape tells me that does not support that block size. I tried 1024 and it worked, but I'm wondering since Tivoli Storage Manager recommends a block size no greater than 256. I would like someone to explain this topic a little more in detail. Thank you in advance for your attention. Gustavo Echenique ------------------------------ Gustavo Echenique ------------------------------ #Informix

Gustavo: So here is the deal with backing up to tape and block sizing. The following is very simplified! Experts be kind! Tape backup systems are also called "streaming tape" backup systems. When you begin writing to a streaming tape, the drive starts running tape past the write head. Ontape begins by writing a header block that is the "TAPEBLK" size. Then it waits until the tape device acknowledges the write was successful before writing the next block. Meanwhile the tape is still streaming past the write head with nothing being written so there is a gap. Those gaps are all the same size (with a few exceptions I suppose). The smaller the write block the more space on the tape is wasted in the inter-block gaps in the data written to the tape. If you could "see" the data on the tape, small block data looks something like this: XXXXXXXXXX XXXXXXXXXX XXXXXXXXXX XXXXXXXXXX XXXXXXXXXX XXXXXXXXXX XXXXXXXXXX XXXXXXXXXX XXXXXXXXXX XXXXXXXXXX XXXXXXXXXX XXXXXXXXXX Double the block size and it looks like this: XXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXX XXXXXXXXXXXXXXXXXXXX In the second set we got 120 X's in less space than the first set stored the same amount of data. On disk, if you write an archive to disk, there is no wasted space, so block size really does not matter. But on tape, it does. Art ------------------------------ Art S. Kagel, President and Principal Consultant ASK Database Management Corp. www.askdbmgt.com ------------------------------

Excellent explanation Art! With this way of graphing, the work of the recorder heads is perfectly understood. What TAPEBLK would you recommend? Thank you very much again! ------------------------------ Gustavo Echenique ------------------------------

Gustavo: I have not used tape in years, but IIRC I used to set TAPEBLK to 2048 (2MB). Important: make sure it is a multiple of your base pagesize (so 2 or 4 depending on your OS). Art ------------------------------ Art S. Kagel, President and Principal Consultant ASK Database Management Corp. www.askdbmgt.com ------------------------------

Shouldn't this be a property of your tape device, i.e. come from your Ultrium documentation? ------------------------------ Andreas Legner ------------------------------

Not used real tapes in years but back in the dark ages I would increase the block size until the 'write' light on the tape unit was continuously on, not very scientific but seemed to work Cheers Paul On 12/22/2022 7:57 AM, Andreas Legner via IBM Community wrote: 010001853a1f8850-ed76e595-561f-475c-87bf-4b2dd15ec439-000000@email.amazonses.com"> Shouldn't this be a property of your tape device, i.e. come from your Ultrium documentation? ------------------------------ Andreas Legner ------... Informix Post New Message Re: Ontape parameters Reply to Group Reply to Sender Dec 22, 2022 8:57 AM Andreas Legner Shouldn't this be a property of your tape device, i.e. come from your Ultrium documentation? ------------------------------ Andreas Legner ------------------------------ Reply to Group Online View Thread Recommend Forward ------------------------------------------- Original Message: Sent: Wed December 21, 2022 08:48 PM

Hi Gustavo, TAPEBLK was used in the past to define the block size that allows you to write to tape. It used to be small since it was based on the value that was accepted by the TAPE device itself. After moving backups to disk, we use a value much bigger to speed up the backups (2048 for example which was way to big on old tape devices at the time) . You cannot go beyong the max value of the block size accepted by your Tape device. You should consult your tape device documentation to get the max value allowed. You can try using the dd command (look at the unix /linux syntax) with a block size to test writing to your device. The maximum value allowed will be your max value allowed using the informix ontapecommand Cordialement, Regards, Khaled Bentebal Directeur Général - ConsultiX Tél: 33 (0) 1 39 12 18 00 Mobile: 33 (0) 6 07 78 41 97 Email: khaled.bentebal@consult-ix.fr Site Web: www.consult-ix.fr Le 21/12/2022 à 23:49, Gustavo Echenique via IBM Community a écrit : 0100018536e0cd6c-ab129e06-c6de-46d3-8ebc-1fd92c1e8252-000000@email.amazonses.com"> Dear colleagues: I need to make backups on tape. I have an external HP LTO Ultrium 6 drive with native 2.50TB cartridges, and my problem is... -posted to the "Informix" group Informix Post New Message Ontape parameters Reply to Group Reply to Sender Dec 21, 2022 5:50 PM Gustavo Echenique Dear colleagues: I need to make backups on tape. I have an external HP LTO Ultrium 6 drive with native 2.50TB cartridges, and my problem is focused on the TAPEBLK parameter, which I had at 2048 when I backed up to disk, but when I want to do it to tape, the ontape tells me that does not support that block size. I tried 1024 and it worked, but I'm wondering since Tivoli Storage Manager recommends a block size no greater than 256. I would like someone to explain this topic a little more in detail. Thank you in advance for your attention. Gustavo Echenique ------------------------------ Gustavo Echenique ------------------------------ Reply to Group Online View Thread Recommend Forward