odd prob for cygwin 'dd' from a character device on network disk

odd prob for cygwin 'dd' from a character device on network disk

[L A Walsh]

I've been using a character device on linux in my
home directory named 'zero' that is a copy of the
'zero' device in /dev:
crwxrwxrw- 1 1, 5 Jun 15  2015 zero

to do read benchmarks using 'dd' (and write benchmarks
using a file named 'null' thats a copy of /dev/null).

I run it "occasionally", but not on a regular basis, since
it stays a bit boring.  Nevertheless, ballpark numbers
consistent with historical norms verify correct network
function (separate from read/write files).  Read/write speeds
at last check a few weeks ago were typical with
reads at 700MB/s and writes at about 300MB/s.

A few hours ago I tried it again due to some strange network
probs where I seemed to be getting file xfer speeds as low
as 200K/s.

I tried the bench script, and its half broken now -- because
I can no longer get anything back from the zero device
on my server via the network.  Locally, I can do 'dd' from
/dev/zero (or the zero file) and it takes a few seconds and
gave about 800MB/s.  So seemed to have been working fine,
but remotely -- still nada... reads 0 bytes from /dev/zero
and about 300MB/s write speed.

Can anyone think of anything that might have changed in
cygwin such that it would know the remote device is a
"/dev/zero".  Wondered if the 'dd' prog might have changed,
but just realize it did same with 'cat' as well.

Anyway -- I'm a bit stumped as to possible causes...
The writing to a remote /dev/null part is still working,
so not sure why one would change and not the other.

If anyone can think of anything, please let me know -- I'm
also gonna ping the samba list and maybe my distro list

Thanks!
-linda

Re: odd prob for cygwin 'dd' from a character device on network disk

[Duncan Roe]

On Wed, Jun 09, 2021 at 06:19:43PM -0700, L A Walsh wrote:
> I've been using a character device on linux in my
> home directory named 'zero' that is a copy of the
> 'zero' device in /dev:
> crwxrwxrw- 1 1, 5 Jun 15  2015 zero
>
> to do read benchmarks using 'dd' (and write benchmarks
> using a file named 'null' thats a copy of /dev/null).
>
> I run it "occasionally", but not on a regular basis, since
> it stays a bit boring.  Nevertheless, ballpark numbers
> consistent with historical norms verify correct network
> function (separate from read/write files).  Read/write speeds
> at last check a few weeks ago were typical with
> reads at 700MB/s and writes at about 300MB/s.
>
> A few hours ago I tried it again due to some strange network
> probs where I seemed to be getting file xfer speeds as low
> as 200K/s.
>
> I tried the bench script, and its half broken now -- because
> I can no longer get anything back from the zero device
> on my server via the network.  Locally, I can do 'dd' from
> /dev/zero (or the zero file) and it takes a few seconds and
> gave about 800MB/s.  So seemed to have been working fine,
> but remotely -- still nada... reads 0 bytes from /dev/zero
> and about 300MB/s write speed.
>
> Can anyone think of anything that might have changed in
> cygwin such that it would know the remote device is a
> "/dev/zero".  Wondered if the 'dd' prog might have changed,
> but just realize it did same with 'cat' as well.
>
> Anyway -- I'm a bit stumped as to possible causes...
> The writing to a remote /dev/null part is still working,
> so not sure why one would change and not the other.
>
> If anyone can think of anything, please let me know -- I'm
> also gonna ping the samba list and maybe my distro list
>
> Thanks!
> -linda
>
nfs / nodev?

Re: odd prob for cygwin 'dd' from a character device on network disk

[L A Walsh]

On 2021/06/09 19:23, Duncan Roe wrote:
>>
>>     
> nfs / nodev?
>
>   
I'm not sure what you mean or are asking.
I'm not using nfs...but cygwin.

The file 'zero' is in the same dir as the file 'null'.
I usually read 'zero' and write to 'null, though
for 1-way testing, I read from file 'zero' on the remote
file system and write, locally to /dev/null.

For other direction write to 'null' and read from
/dev/zero locally.

Re: odd prob for cygwin 'dd' from a character device on network disk

[Duncan Roe]

On Thu, Jun 10, 2021 at 08:20:30PM -0700, L A Walsh wrote:
> On 2021/06/09 19:23, Duncan Roe wrote:
> > >
> > nfs / nodev?
> >
> I'm not sure what you mean or are asking.
> I'm not using nfs...but cygwin.
>
> The file 'zero' is in the same dir as the file 'null'.
> I usually read 'zero' and write to 'null, though
> for 1-way testing, I read from file 'zero' on the remote
> file system and write, locally to /dev/null.
>
> For other direction write to 'null' and read from
> /dev/zero locally.
>
>
When you said you were accessing zero over the network, you didn't say how so I
suggested if you were using nfs then nodev might be the culprit.

How are you accessing files aver the network?

I suspect that whatever mechanism you are using has the equivalent of the nfs
nodev feature (part of nfsmount, may be specified in fstab) and the nodev
equivalent is turned on in your case.

Re: odd prob for cygwin 'dd' from a character device on network disk

[L A Walsh]

On 2021/06/11 18:32, Duncan Roe wrote:
> On Thu, Jun 10, 2021 at 08:20:30PM -0700, L A Walsh wrote:
>   
>> On 2021/06/09 19:23, Duncan Roe wrote:
>>     
>>> nfs / nodev?
>>>
>>>       
>> I'm not sure what you mean or are asking.
>> I'm not using nfs...but cygwin.
>>
>> The file 'zero' is in the same dir as the file 'null'.
>> I usually read 'zero' and write to 'null, though
>> for 1-way testing, I read from file 'zero' on the remote
>> file system and write, locally to /dev/null.
>>
>> For other direction write to 'null' and read from
>> /dev/zero locally.
>>
>>
>>     
> When you said you were accessing zero over the network, you didn't say how so I
> suggested if you were using nfs then nodev might be the culprit.
>
> How are you accessing files aver the network?
>
> I suspect that whatever mechanism you are using has the equivalent of the nfs
> nodev feature (part of nfsmount, may be specified in fstab) and the nodev
> equivalent is turned on in your case.
>   
----
    Was afraid that's what you meant...don't know of such an option
with samba, not to mention using the same version of samba now,
as for ages.

    Using smb/cifs -- a mounted samba share with my home directory mounted
as drive 'H'.

The device files are created in my home directory (on linux)
as files 'zero' and 'null'.

I don't know of any equivalent 'nodev' option in samba -- but
regardless, I'm not sure what has changed.  I'm still running the
same samba that I have for over a year -- my kernel might be
different, but I don't think there's been any change
to '/dev/zero' -- but in the same directory, writing to
the file named 'null' still works.

*sigh*