schrieb Adrian Reyer am 10.07.2011 14:43 (localtime): > Hi Harry, > > On Sun, Jul 10, 2011 at 01:38:52PM +0200, Harald Schmalzbauer wrote: >> of a average transfer rate of 65MB/s makes me worrying about massive >> repositioning. > > AFAIK LTO-Drives have adaptive speeds compared to older technologies. If > the data comes in slower, the drive will just run slower on a somewhat > constant speed. No more stop-and-go.
Hi Adrian, thanks for your reply. I read about throttling capability, but `mt status` shows drive state "at rest" even during active transferes. The server is at remote site, so I can't hear any mechanicals, but I guess "at rest" means stop, thus my worries about extensive repositioning. >> Can I optimize my setup so that there won't be so many new files written >> on tape? Or should the creation of a new file mark been done without >> interruption of the transfer, and there's something wrong with my setup? > > Do you use 'Spool Data = yes'? > To my understanding you can run multiple jobs to storage the same time, > but they end up interleaved. Spooling the data will write full jobs or > at least bigger chunks of a job in one run. I have no backup jobs using the tape drive, so no spool is in use. I only use the tape drive for migration (or sometimes copy) jobs. And in the disk-pool I use "Use Volume Once = yes", so every job has it's own file without interleaved data, which has exactly the size the job summary reports. Do you know if marking a "new file" on tape interrupts the LTO drive from streaming? Perhaps it shouldn't interrupt streaming, and writing many files for one job is a well choosen design, and I'm suffering from some other misconfiguration which leads to interruption on marking new file. If it's technically not possible to keep the drive streaming while marking a new file, then I'm interested in tweaks how to avoid hundreds of "new file" marks per backup job. Do others see 208 files after 200G writte on tape? Wild guess: If one file is marked every 1GByte written (wich takes max 12.8sec in my case), and this file mark interrupts the drive for round about 4 seconds, then my transfer rate decreases from the usual rate for uncompressable material of 80MB/s by 25% to ~60MB/s. That would exactly represent the numbers I'm seeing here... Which means the drive is only streaming 75% of the time, the rest is used for repositionings :-( Maybe this was not an issue with slower tape drives. LTO2 would only suffer from about 6% performance loss, if my wild guess has any truth... Thanks, -Harry
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