Local disk to disk Rsync taking an hour longer than disk to remote

Tony Abernethy tony at servacorp.com
Mon Jul 16 21:02:27 GMT 2007

>From an old old old-timer
The first disks that IBM came out with were effectively the same 
speed as card readers and line printers. For unblocked records.
Disks are NOT asynchronous. They spin at a very predictable
Rate and timing are extremely different based on whether the 
Head is in the right place just before or just after the point
In time when the data comes by.
The exact parameters of disk caches (all of them) can do all
Sorts of strange things to the timings.
Even the where on the disk the files are can matter.
With a bit of experimenting, you should be able to get some
Very real and violently counter-intuitive results.
Optimized for known contention can mess up badly faced with
unknown contention  (two disks on same anything)

> -----Original Message-----
> From: rsync-bounces+tony=servacorp.com at lists.samba.org 
> [mailto:rsync-bounces+tony=servacorp.com at lists.samba.org] On 
> Behalf Of W Smith
> Sent: Monday, July 16, 2007 3:36 PM
> To: rsync at lists.samba.org
> Subject: Local disk to disk Rsync taking an hour longer than 
> disk to remote
> Back in June I posted about the trouble I've been having 
> backing up some local directories and I'm no further ahead 
> than back then.
> Link for that discussion:
> http://lists.samba.org/archive/rsync/2007-June/017882.html
> In summary: I'm copying nearly a million small files from the 
> main disk in a server to another disk in the same machine.
> Still on this server, but at a different time, I am backing 
> up the same million files to a remote server which is 
> completed massively quicker and I just can't get my head 
> around why this should be.
> Here are some new stats I got whilst using "time" to measure 
> the difference between the two processes.
> Local backup
> -------------------
> Number of files: 1060320
> Number of files transferred: 2233
> Total file size: 26814206753 bytes
> Total transferred file size: 58711290 bytes Literal data: 
> 58711290 bytes Matched data: 0 bytes File list size: 47383393 
> Total bytes sent: 106196771 Total bytes received: 44680
> sent 106196771 bytes  received 44680 bytes  12914.54 
> bytes/sec total size is 26814206753  speedup is 252.39
> real	137m5.932s
> user	0m16.843s
> sys	125m35.697s
> Remote backup
> -----------------------
> Number of files: 1060823
> Number of files transferred: 1758
> Total file size: 28255934663 bytes
> Total transferred file size: 63027228 bytes Literal data: 
> 63027228 bytes Matched data: 0 bytes File list size: 47404505 
> Total bytes sent: 110514244 Total bytes received: 35180
> sent 110514244 bytes  received 35180 bytes  89045.05 
> bytes/sec total size is 28255934663  speedup is 255.60
> real	20m40.908s
> user	0m11.344s
> sys	0m22.644s
> Sure there are a few less files on the remote backup, due to 
> the scripts running at different times but this can't explain 
> the hour difference in runtime can it?
> I've studied the rsync man page for hours, trying to find 
> some elusive option to speed up local performance to no 
> avail. I've also tried Unison and rdiff-backup, hoping that 
> they might be better for local copying, but nothing comes 
> close to rsync remote backup speeds.
> At this stage I'm close to giving up and am considering 
> forgetting local backups and getting another server to have 
> two remote backups instead, which wouldn't be a bad thing.
> My last hope is in the wisdom of this mailing list... :)
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