On 2015-05-17 02:48 AM, Florian Rist wrote:
>
>> So you will need more than one tape for a full backup and this will
>> need
>> manual intervention for changing tapes.
> Yes, I know, as long as this is supported (and as far as I can see it
> is) by Bracula that's fin. I remember it was difficult using Amanda in
> 1996 or so.

Autochangers are well supported by Bacula.  Manual tape changes with 
notification emails can be set up as well - we ran that for quite a 
while before I got my changer.
>
>> If this is not a problem for you Bacula and an LTO drive is a
>> feasible solution. Otherwise you should probably think about a tape
>> library for this work.
> Yes, a library would be good, but I cant afford one now. Maybe I could
> get a old used library and replace the drive by a new one...

I've had good luck with used libraries overall.  Cleanliness is super 
important - if it's filthy on the outside and has lots of dust bunnies 
it's not a good candidate, but I've got a 10+ year old IBM LTO library 
here that's working great, and a 5+ year old Neo 2000 that's likewise 
working great.  While I could certainly do with newer (higher capacity) 
drives all my tape drives are working well too.

>> ​Yes, You can have full/differential/incremental backups in a
>> ​hard disk and then write once a week to tape. This is commonly
>> known as disk-to-disk-to-tape (D2D2T) backups.
> OK, in this case how much hard drive storage would I need? Enough to
> hold the full backup ore just a few TB for the weekly incremental
> backups?

Depends what you want to do - you can use spooling to keep the tape 
drive fed at its max rate, though no new data will be flowing from the 
client to the storage daemon when things are writing out - your backup 
speeds will be reduced but your tape drive will work a lot better.  If 
you have enough space on disk to write out the entire thing and then 
copy to tape later you won't have that problem.
>> ​What do you mean about "slow Network"? Could you be more specific?
> 100Mb/s and not the best topology, a few PC via VPN through 100 MBit/s
> LAN
>
>> Are your data go across wan links?​ There are lots of known cases
>> with Bacula working across wan links with no problems.
> No WAN, I just wondered if I need to ensure a minimum data throughout
> for the LTO. I member some problems in this respect with the DDS drive.
>
Yes, there is definitely a minimum throughput for LTO drives.  If you 
aren't writing from local storage then you almost certainly won't be 
able to meet it for anything at all modern.  LTO-3 was the last 
generation that could be fed by a gigabit ethernet link (full speed is 
80MB/sec), newer technologies have much higher throughput rates.  As 
mentioned above, the way to solve this is to write out to local disk 
storage first and then copy to tape.  If you're using any of the more 
recent LTO versions (5/6) you really need to make sure your disk setup 
on your backup storage server is capable of keeping up with the tape 
drive - most consumer hard drives top out at about 120MB/sec for 
sequential reads and much less than that for random I/O (such as having 
backup jobs writing to the disk at the same time as the tape drive is 
reading from it)

The most flexible approach would be to have enough local storage for at 
least one full backup from everything plus a healthy amount of 
differentials and incrementals, that way most restores don't touch the 
tapes unless something Really Bad Happens.  If that isn't practical then 
Bacula can be configured to spool to tape (I do this with my 
incrementals as they have a hard time pushing data fast enough to 
maintain my drive's write speed due to files being scattered around the 
source disks).

When using spooling you give Bacula some space, it writes till it hits 
whatever your max spool size is, then it stops spooling and writes out 
that data to tape, when done it erases what it had on disk previously 
and continues spooling data from where it left off. As mentioned above 
there is an impact on your overall backup times with this as no new data 
will be flowing in during the periods when Bacula is writing to tape, 
however it'll keep your tape throughput in the 'happy' zone.

Bryn

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