Zitat von Alan Brown <ajb2 AT mssl.ucl.ac DOT uk>:

> On 21/08/12 16:04, Dan Langille wrote:
>
>> ###
>> The DLT drive default data block transfer size is 4KB (4096 bytes).
>> To achieve better performance, adjust block size to 32K bytes or
>> higher when using a fixed block device.
>> ###
>
> What you want to know is how big it can go - and the only way to  
> know that is to experiment.
>
> Assuming your DLTs are DLT8000, 12 hours is about spot-on for the  
> raw capacity and speed of the tape (40GB raw + 7GB/hour)
>
> I'm seeing unspool speeds of about 150MB/sec to LTO5 using 2MB block  
> sizes (that's max, smaller block sizes get used too), and tests show  
> the spool (raid0 4 * Intel 64GB SLCs) is capable of something like  
> 800MB/s r/w with several streams running (1400MB/s single sustained  
> read to /dev/null)
>
> That means there's some room for improvement in despooling speed,  
> but the big bottleneck at the moment is disk-fd and fd->sd, not  
> sd->tape - the best achieved there is a sustained 52MB/s and that  
> virtually maxes out a 1Gb/s NIC. Even if the network block sizing is  
> optimized, I need to look at 10Gb NICs and for simultaneous  
> spool/despooling.

We plan to takle this one with parallel running jobs doing spooling to  
SSD and despooling to tape. As far as i understand spooling/despooling  
can happen in parallel if using different jobs.


> WRT "offsite backups" - I'm more inclined to use a good firesafe in  
> another building than pass media to a 3rd party company. Far too  
> many people backup to tape but then don't take care of the media.

Our's are in a Bank safe at the other end of the town and in the  
future they are also encrypted thanks to Bacula :-)

Regards

Andreas



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