[Dovecot] dsync is SLOW compared to rsync

[Linda Walsh]

Jeff Gustafson wrote:
> On Fri, 2012-03-23 at 19:02 +0100, Christoph Bußenius wrote:
>   
>> Hi,
>>
>> maybe try "dsync -o mail_fsync=never".
>>     
>
> 	That didn't seem to make much of a difference. On a 3.1GB backup it
> shaved off 5 seconds. dsync's time was over 6 minutes with or without
> the mail_fsync=never. rsync copied the same 3.1GB mailbox in 15 seconds.
> 	It seems to me that dsync *should* be able to be just as fast, but it
> currently is spending way too much time doing something. What is it?
> 				...Jeff
>   
---

Next -- bench "cp -ax", against rsync -axHAX when it has to copy >75% of 
the data (cp ~6-8x speed).  But for file speed, 'dd' is king, as it can 
use large buffers (~16MB gives best results on my local Gbit network), 
but it
misses all those pesky acls and extended attrs, not to mention file 
perms...*sigh*   Compare that to the I/O done 4k at a time by many older 
utils...

If I'm writing to the LOCAL HD, instead of the network, then a 1GB-4GB 
buffer size gives best results (1GB/s raid5).  Small buffers are such a 
PITA!