On Aug 21, 2012, at 12:38 PM, Alan Brown <ajb2 AT mssl.ucl.ac DOT uk> wrote:

> 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)

In my case, DLT7000.

> 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.
> 
> 
> 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.

All my backups are in my basement. Including the tapes. I really should move 
the latest full backups somewhere else. 

-- 
Dan Langille
http://langille.org/


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