Andreas, Thank you for that helpful explanation. I recognize that Maximum File Size and Maximum Block Size are different. Glad to hear that I can leave Maximum Block Size alone. For Maximum File Size, I'll try making that change when I can restart my storage daemon next. Initially I was confused as I figured this would relate to the files from the client that are being written, however it appears this is more about how bareos does buffering of data to the tapes.
On Monday, April 28, 2025 at 5:02:55 AM UTC-5 Andreas Rogge wrote: > Hi Jon, > > Am 14.04.25 um 19:36 schrieb Jon Schewe: > > I have not set the Maximum File Size for my tape devices as I assumed > > this was only for file based backups. I now see https://docs.bareos.org/ > > bareos-19.2/TasksAndConcepts/AutochangerSupport.html#tapespeed-and- > > blocksizes points to changing this value. Is there a recommendation for > > LTO-8 and LTO-9 devices? > > My personal recommendation for newer LTO generations (i.e. LTO-6 and > newer) is to set Maximum File Size to 250 GB. > > Just to add a bit of background information: > As you already know tapes basically contain a stream of blocks. However, > historically (i.e. when using tar/cpio directly) you would put multiple > files onto a tape. Therefore end-of-file marks are placed on the tape > and the drives can fast-forward to these. > Bareos makes use of this by putting end-of-file marks onto the tape at > least every Maximum File Size bytes. > When putting such an end-of-file mark into the tape, there is also a > guarantee that the data including the mark was actually persisted to the > tape (and is not just in the drive's buffer). > > The downside of this is, of course, that the tape buffer is flushed > every time a mark is written. As modern drives have pretty large caches > (1 GB and maybe even more), the drive will never come up to speed as > you're basically synchronously flushing the buffer every time before it > gets full. > > > It looks like changing the Maximum Block Size can be a challenge to keep > > compatibility with older backups. Does changing this make a large > > difference in performance and make it worth the risks? > > Please do not mix up Maximum File Size and Maximum Block Size. These are > totally different things. > Maximum Block Size nowadays defaults to 1 MB. Outside of testing there > should be no need to ever touch this parameter. > Read compatibility was also added to Bareos 23: When the SD encounters a > block that is larger than its configured Maximum Block Size, it will > automatically retry with 1,2,4,8 and 16 MB block size. > So while the warnings in the whitepaper about changing the Maximum Block > Size are still valid, restore should still work even with a > misconfigured SD. > > Best Regards, > Andreas > > -- > Andreas Rogge [email protected] > Bareos GmbH & Co. KG Phone: +49 221-630693-86 <+49%20221%2063069386> > http://www.bareos.com > > Sitz der Gesellschaft: Köln | Amtsgericht Köln: HRA 29646 > Komplementär: Bareos Verwaltungs-GmbH > Geschäftsführer: Stephan Dühr, Jörg Steffens, Philipp Storz > > -- You received this message because you are subscribed to the Google Groups "bareos-users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/bareos-users/2c4ac847-0355-418a-b9c5-20d678c4aaa8n%40googlegroups.com.
