Fwd: [opensuse] HP Ultrium LTO Compression
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On Thu, Apr 28, 2016 at 2:31 PM, Darin Perusich <darin@darins.net> wrote:
What is the block size your backup software using to write data to the tape? The block size will effect not only the rate at which data can/will be written to tape but also the amount of data which can be written to a single tape. In a past life I used Amanda to backup systems to LTO2 and LTO3 libraries and with the default 32k block size saw horrible performance, nowhere near what the devices could provide. After much trial and error determined that setting a block size of 128M or 256m, it escapes me, was needed for the drives to perform at their maximum rate. This certainly limited the amount of data I would write to tape, but didn't care too much since these were attached to like 12 tape libraries.
I don't know that I agree the block size affects storage capacity. Maybe it does. I've never used such large blocks. Last time I did significant LTO performance testing from opensuse (SuSE at the time I think) was 10+ years ago with LTO Gen 1 drives. I used 128M via something like: tar ... | mbuffer -m 128M -p 90 -o /dev/st0 (I don't have my old scripts handy so I don't have the exact syntax.). For a LTO-5 drive you might need a multi-GB buffer or larger to keep the tape streaming. That class of drive eats a lot of data in a hurry. But the blocksize is NOT 128M in the above. mbuffer understands tape blocks. The default blocksize is 8K. There is a -d arg that says to ask the drive for its default blocksize. The above command buffers up a lot of 8K blocks in RAM, then sends them to the tape drive when the 128M RAM buffer is 90% full. It keeps sending data to the tape until the buffer empties out. It doesn't resume sending data until the buffer is 90% full again. The goal is to keep the drive from "shoe-shining" too much. If you listen to the drive and you have a lot of shoe-shining you know you need to use a bigger buffer. That does NOT mean you need a bigger block size. Greg -- Greg Freemyer www.IntelligentAvatar.net -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org
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Greg Freemyer