On 1/23/2015 2:33 PM, Heitor Faria wrote:
>> On 01/23/2015 12:22 PM, Radosław Korzeniewski wrote:
>>
>>> If you are using a vchanger then I guess it is a disk only backup, so why
>>> do you spool data? It is not required but making you backup slow down at
>>> least 2 times then standard job.
>> It's 2 times slower if your spool/despool is strictly sequential and the
>> same size pipes go in and out. If you have 10 clients spooling over a
>> 1Gb/s link, that's roughly 10MB/s/client. Iostat clocks ext4/basic sata
>> drives at around 110MB/s write speed, so despooling is 10 times faster.
>> If only the clients could keep the pipe full, it could be ~10 times
>> faster than the "standard" job. In a purely hypothetical perfectly
>> spherical world of uniform density, obviously, but still: no, 2x slow
>> down is not how it really works.
> Even though, IMHO, spooling disks backup is just "muda" (Japanese Term): 
> http://en.wikipedia.org/wiki/Muda_(Japanese_term)

No. It is not wasteful if it serves a purpose. The goal is to get the 
client's part in the job done faster. Fast storage is expensive. A 
shared spool area on fast disk gets the clients part done faster, and 
then the SD can de-spool to slower (and cheaper) volume file storage 
without affecting the client. Using spooling for disk volumes is exactly 
the same reasoning as using it for tape volumes.


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