Renaming (with 'mv') very large files is SLOW

[René Berber]

On 1/31/2022 8:59 AM, Eliot Moss wrote:

> On 1/31/2022 9:52 AM, cygwin@kosowsky.org wrote:

>> I tried renaming some very large files (20-40 GB) using: mv
>> <oldname> <newname> without changing the directory of course.
>> 
>> The process took about 10-20 minutes with Task Manager showing
>> disk activity of 100+ MB/s.
>> 
>> Is there something about such large 'renaming' that actually
>> results in the file being really moved (aka copied) rather than
>> just renamed?
> 
> The two places are probably on different volumes (loosely, different
>  disks). That requires a physical move, even under Linux.  Your
> volumes seem a bit slow to access - is one perhaps across a slow
> network?  The rates you cite suggest movement of 50Mb/s (50Mb read +
> 50Mb write = 100Mb overall).  For 40 Gb that should take 40Gb / 50Mb
> = about 820 secs = a little under 14 mins.
> 
> (When I say your volumes are slow, I speak from the luxury of having
> a 2Tb solid state drive!  Actually, those speeds may be reasonable
> depending on the nature of your system.)
> 
> If the two locations are on different drives, there's no real
> avoiding this.

Nope, I've also complained about this (long ago), if the two locations
are the same remote drive... Cygwin moves the entire file over the network.

I ended up writing my own Samba mv command.
-- 
R. Berber