[tech] Where is /away, was "Re: [ucc] Minutes of Meeting on Sunday, 24th November 2013"

[Sam Moore]

On Sun, 24 Nov 2013, David Adam wrote:

> On Sun, 24 Nov 2013, Erin Steicke wrote:
>> Committee Meeting for 2013-11-24
>> -----------------------------------
>> Machine Technical Reports
>> -------------------------
>> Servers
>>  - SAN got sick on 2013-11-20 which somehow stopped Mylah exporting /away
>>    - Even though /away is actually /volumes/space/home/away on nortel
>>    - Thanks [DAA] for fixing with magical powers
>
> I'm not sure where this idea came from - I see [SZM] mentioned it on IRC,
> but I didn't have time to correct him.
>
> /away is /backups/restored/space/away on Mylah, and the /backups volume is
> on the SAN.

tl;dr /away is actually /backups/restored/space/away/home but 
/space/away/home is a symlink to it, and /vol/space is on nortel.

Alright, I feel very stupid but since the majority of wheel seemed to be 
of the same opinion as me (or at least were too lazy to correct me despite 
several blatantly wrong statements on my part to this list and elsewhere), 
I want to reveal the source of confusion here.

Extracts from /etc/fstab on mylah and exports on nortel show that /space 
is definitely on nortel and /backups is definitely on the SAN.

mylah:
/dev/mapper/sanspace-backups    /backups        ext3    auto,user_xattr,acl     0       2
nortel.ucc.gu.uwa.edu.au:/vol/space /space nfs  nfsvers=3,auto,rw,tcp,nosuid,nodev,rsize=8192,wsize=8192,intr 0 0

nortel:
/vol/space -sec=sys,rw=<snip>:mylah.ucc.gu.uwa.edu.au:<snip>

Extracts from /etc/exports on mylah show that it is exporting 
/space/away/home to all machines except Red (note that Red hasn't been in 
use for months).

/space/away/home        pinball(rw,no_root_squash,no_subtree_check,sync)
...
/backups/restored/space/away/home 	red(rw,no_root_squash,no_subtree_check,sync)

Now, at the time I thought "/away must have been on the SAN, but got 
moved and no one bothered updating Red". And then I checked for a symlink 
just in case:

/space/away:
drwxr-xr-x  3 backups backup 4.0K Jun 26  2012 away

/backups/restored/away:
drwxr-xr-x 3 root wheel 4.0K Jun 26  2012 away

What I failed to do was check /space/away/home itself. Had I done this, 
the situation would have become obvious:

lrwxrwxrwx 1 root wheel 38 Jun 26  2012 /space/away/home -> ../../backups/restored/space/away/home

So. Everything points to /away being on nortel, until you find out that it 
is actually a symlink on nortel that points to the SAN.

There is a folder /space/away/home_partial_rescue.
I suspect that the "good reason" is that this folder used to be 
/space/away/home and after /away was moved to the SAN the symlink was made 
because no one could be bothered updating /etc/exports on mylah and 
/etc/fstab on everything.

I'm sure there were emails to this list at the time this was done and 
you've all secretly been laughing at me, but if there weren't then here 
you go.

I'm not sure how a symlink on an NFS filesystem pointing to a physical 
device affects performance, but I'm not going to change all those 
config files.