SCP with Resume Feature

[rapier]

On 4/6/21 10:27 AM, rapier wrote:
> 
> 
> On 4/5/21 6:22 PM, Damien Miller wrote:
>> On Sat, 3 Apr 2021, Demi Marie Obenour wrote:
>>
>>> On 4/1/21 1:50 PM, rapier wrote:
>>>> Howdy all,
>>>>
>>>> I know development on SCP is discouraged but being that it's still
>>>> in wide use I thought I would do some work some of my users have
>>>> been asking for and allow SCP to resume from a partial transfer.
>>>
>>> Would it be possible to instead reimplement SCP in terms of SFTP, and 
>>> then add
>>> this feature to SFTP?  My understanding is that such a 
>>> re-implementation is
>>> something many people have wanted for quite a while.
>>
>> Yes, and there are patches to do this awaiting review:
>>
>> https://github.com/openssh/openssh-portable/pull/194
> 
> That would be awesome. The more I work with the SCP code the more I've 
> come to dislike it.

Looking at the performance - on my systems sftp seems to be a bit slower 
than scp when dealing with a lot of small files. Not sure why this is 
the case as I haven't looked at the sftp code in years.

For 100MB over 2666 files:
[rapier test] time sftp -r me at foo:~/testdir testdir
real	0m10.902s
user	0m1.532s
sys	0m2.679s

[rapier test] time scp -r me at foo:~/testdir testdir
real	0m5.915s
user	0m0.883s
sys	0m1.497s

A test with 6.8G over 19 files has nearly identical performance.

That said, this may be "good enough" for people or it could be an issue 
with my somewhat older test hosts. Dunno but I wanted to mention it.