Steven Hammond wrote (2017/05/31):
> 1. Is it safe (Bacula 7.XX) to set the block size to something other
> than 64K?
You have to try it, but it should be safe in Linux. Write data with
bigger blocks and read them back with source comparison. btape should
do the job too.
> 2. Does increasing the block size increase the throughput? (2 x 3.6Ghz
> PROCS - 24 cores, 32GB RAM, 6x600GB 15K RPM SAS, external SAS / HP LTO-5)
If the disks are not a bottleneck, then in Linux it should increase the
throughput very much. Yes, you have very good disks, but experiences say,
that you really need SSD disks to take full advantage of LTO-5.
> 3. Are there any down sides to increasing the block size? (e.g.,
> existing tapes created)
Lower portability. If you want to read the tape back, you need a system,
which does support atleast the same block size, which depends on used
operating system, host adapter and its driver. It also depends on tape
drive, but just do not use block bigger than 8 MB and you are safe.
However, it is recommended do not use blocks bigger than 2 MB and please
do not exceed it if you do not know what you are doing.
> Despooling speeds avg 60+ MB/s. I also have a quad nic bonded
It is too low for LTO-5. It is at the lower limit before tape
shoe shining, problably with some tape stops already here.
The real limit is 47 MB/s for HP and 40 MB/s for IBM, but no
guarantee it is correct.
> O/S: Ubuntu 17.04 (so we could get a later version of bacula without
> compiling from source)
>
> I'm not overly concerned about the speed (everything backs up over night
You are concerned, because you want to protect your tape drive from
a malfunction.
> fine) but I was hoping to get over 100 MB/s seeing that the LTO-5
> theoretically can go up to 144 MB/s.
Yes, my typical speeds with LTO-5 are 140-280 MB/s on FreeBSD with
64 KB blocks, but FreeBSD is not so sensitive to block sizes as is Linux.
> Any tips would be greatly appreciated.
Yes, really try to do something with increasing tape write speed and do
not go under 100 MB/s even in low peaks.
--
Rudolf Cejka <cejkar at fit.vutbr.cz> http://www.fit.vutbr.cz/~cejkar
Brno University of Technology, Faculty of Information Technology
Bozetechova 2, 612 66 Brno, Czech Republic
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