[kwlug-disc] Was cronjob / btrfs scrup [Was: Re: What is all this about systemd?]

[B.S.]

On 14-10-28 01:56 PM, Khalid Baheyeldin wrote:
> On Tue, Oct 28, 2014 at 1:51 PM, B.S. <bs27975 at yahoo.ca> wrote:
>> It seemed that vbox snapshots are fine for vm 'surviving' functionality on
>> hardware that works throughout. It didn't seem fine if you yank the original
>> disk away - the only way to accomplish that was via an underlying fs
>> snapshot facility.
>>
>> You understand differently?
>
> I did not test a case where I changed the original disk, so I can't
> comment on what happens one way or the other.

Silly me. Just realized what I'm really talking about is a disk mirror 
(Raid1) here - no need to play with snapshots. (Either vm or fs.)

I suppose there'd be a performance hit with btrfs checksummed over 
snapshots, but presumably also less complexity, let alone more timely 
alert of any hardware issue. (?)

In poking about, it seemed that such a mirror becomes self-healing. A 
spot goes bad, checksum fails, things get recopied. Interesting.

Not for every use case but I could see it for vms. e.g. OS drive failure 
not atypically means hardware change, so one's mondoarchive may be as 
sufficient as a mirror - given the time needed to source / acquire 
hardware, likely OS evolution since first install, and so on. A vm 
however, being plug and play, you just want to ... well, plug and play.

And not a business solution, where uptime for users is more paramount. 
And I'll guess there is a vm mirroring / other more sensible solutions 
for vm farms.