[sheepdog-users] Sheepdog 0.80: Queries and feedback

[Struan Bartlett]

Hi

Having been trialling sheepdog for a number of days now. It's a really 
good concept, and has moved on a lot since the last time I tried it 
(around 0.40 version). After a fair few hiccups getting it properly set 
up and working, version 0.80 is working reasonably well. I'd like to 
offer some initial feedback on some of the challenges I faced:

1. The README says you need a minimum of 3 nodes, which must be x86_64. 
Sheepdog compiles for i386, and it appears possible to format a cluster 
with 'dog cluster format -c 2' and I seem to have been able to run a 
cluster with two copies, on i386, quite stably. Is this line in the 
README just out of date? If so this is misleading and it would be 
helpful to correct it.

2. Having formatted a cluster with 'dog cluster format' I am not aware 
of a way to determine the format options used (e.g. number of copies). 
It would be helpful if e.g. 'dog cluster info' would display this 
information.

3. I couldn't find documentation of the existence/functionality of the 
sheep gateway option anywhere on 
https://github.com/sheepdog/sheepdog/wiki or 
http://www.sheepdog-project.org/doc/. Maybe I missed it (though I have 
grepped the former and searched the latter). This is such a useful 
option, that it does sheepdog a disservice that it's not highlighted 
better. The manpage only says '-g make the progam run as a gateway mode' 
which doesn't explain what gateway mode is. In the end, I found out by 
emailing this list. It would be helpful to have this option better and 
more widely documented.

4. The manual/help says that 'dog vdi check <vdi>' must not be performed 
on an actively used vdi, presumably because if it has to repair the vdi 
it could cause corruption. If that's the case, it might be helpful if it 
prompted the user and gave a warning before beginning. It might also be 
helpful if 'check' were renamed 'repair' (to avoid the ambiguity). I'd 
also suggest a pure 'check' option, that does not repair. This would all 
be more akin to what an fsck user would expect. The same comments go for 
'dog cluster check' too.

5. The manual/help says in bold letters: "Remember: DO NOT shut down any 
of node before deactivating the cluster! DO NOT shut down / kill a node 
after the other.". Yet isn't the point of sheepdog to be a distributed 
highly available storage system, and isn't it intended to withstand 
individual nodes going down, or crashing, or being shut down by errant 
sysadmins? If so, then I'm finding this warning misleading and 
off-putting. Unless I misunderstand, sheepdog *should* be resilient to 
rebooting of a limited number of nodes, depending on the total number of 
nodes, and the number of copies, shouldn't it? It would be helpful to 
clarify this as there may be times one needs to shut down the cluster 
safely, after a limited number of nodes have already crashed (and the 
data in the cluster is therefore still valid).

That's my initial feedback. If I can reproduce the setup hiccups I had 
on the latest version of sheepdog, I'll submit reports about that 
separately.

Kind regards

Struan

-- 

Struan Bartlett
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