Suggestion for Handbook

[Adam Vande More]

On Fri, Jan 6, 2012 at 11:17 PM, Benjamin Kaduk <kaduk at mit.edu> wrote:

> I think dd would be preferred precisely because it does not use sparse
> files -- all blocks for the image will be allocated.
>
> If a sparse file was used, and the physical disk became close to full,
> then when the system goes to make a write to the image and the backing file
> cannot be grown, things are unlikely to fail gracefully.
>

A full image imposes other penalties and drawbacks.  If you use a modern
hypervisor, it's default backing store will be some type of glorified
sparse file(vmdk, vdi, qcow2 -- at least AFAIK on qcow2).  I would venture
to guess that is because those communities are aware of the advantages and
disadvantages of each with sparse files chosen consistently as the default.

Furthermore, this is the error you get when writing to an overcommited
sparse file:

No space left on device

galacticdominator# diskinfo /dev/md0
/dev/md0        512     1073741824000   2097152000      0       0
galacticdominator# diskinfo /dev/zvol/zoot/usr/home/zvol-test
/dev/zvol/zoot/usr/home/zvol-test       512     5242880 10240   0       0

So it seems a sysadmin ought to be able to deal with that.


-- 
Adam Vande More