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Rumko wrote:
> On 6/22/06, Michel Meyers <[EMAIL PROTECTED]> wrote:
>> Both could be argued: Is performance really better when your backups
>> system is reading from disk and writing to it simultaneously? Probably
>> not. And given the performance hit you take when during those
>> simultaneous reads/writes, your backup system might actually start
>> thrashing and not keep up with the data rate required to feed your tape
>> drive. The result of that would be the dreaded shoe-shining, the exact
>> thing that data spooling is supposed to cure. (I'm pretty sure my backup
> I was more thinking like this:
> When it reaches the specified max spool size it starts despooling as
> usual, at the same it is also spooling new data. BUT if sd runs out of
> data (spooling is slower than despooling) it stops writing until it
> fills the spool to the max spool size.
I understood that. The problem is that if your system can barely
read/despool fast enough to feed the tape (like mine) it may not do
anything else. The fact that Bacula would continue spooling new data
would overpower my backup server (writes to a drive are traditionally
slower than reads plus the drives cannot read continuously any more but
need to jump between read positions and write positions) and, being
unable to read the already spooled data at sufficient rate then, cause
shoe-shining on my tape drive. That's why I'd prefer to see this feature
optional.
>> fine tunable concerning the acceptable data rates (ie settings like:
>> "stop spooling if read rate goes below XXXX" or "limit spool rate while
>> despooling to XXXX" ...).
>Hm, I believe that this would be an overkill, whats wrong with
>simplicity?
Nothing's wrong with simplicity. However, if you have a server that
really cannot handle simultaneous despooling and spooling at full speed
the tuning possibility would be nice to have (nothing more, nothing
less). Without it, you're just going to have to disable 'continuous
spooling'.
Greetings,
Michel
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