Power Cut

[Tom Lawrence]

We live in the Swiss Alps and are subject to power cuts which are not always easy to anticipate and make clone back-up even more essential.

We have successfully executed a Full clone and a Smart clone, but what would be the likely effect if we had a cut part way through either?

Apart from troubleshooting, is it best practice to occasionally execute a full clone after the first?

[dnanian]

I'd probably suggest a full copy if you had a power failure, yes. But, more than that, I'd suggest an uninterruptible power supply!

[Tom Lawrence]

I'd probably suggest a full copy if you had a power failure, yes. But, more than that, I'd suggest an uninterruptible power supply!

Thanks David. As an individual I cannot afford to guarantee my power supply. Even 5 minutes guaranteed supply after a power cut would cost circa $400, time only to quit and close down which I believe is not possible with cloning.

To quote: while in the act of making/updating a clone you actually have NO backup! A power outage at that time or a large surge or a lightning strike *could* render both drives (source and target) useless – all data lost.

My original question which you did not answer was: is this true? ; and, secondly,would both drives be wiped out even with a Smart update?

I have assumed that the quote is indeed true and that for true peace of mind I will need a second clone on a separate and additional drive,disconnected during the cloning process.

in the meanwhile, Smart updates which take a fraction of the time reduce the risk considerably. Clearly, with the short time to do a Smart update, I can usually predict weather and avoid peak electricity demand periods.

I believe it is best to face up to the double jeopardy of cloning-the possibility of losing two drives-if a power cut hits during the process. In no way does this weaken, at least in my view, the case for cloning. My main reason for the clone is to have cover when doing a lengthly TTP defragmentation exercise, for example.

Your further comments would be appreciated.

[dnanian]

Actually, a 20 minute UPS costs around $100 these days (I recently bought a 35 minute one for $99), so you might want to take another look. And yes, you can simply stop the copy at any time.

If you're not rotating backups, then yes -- a power failure could destroy both the source and backup. This is true of non-clones as well as clones, if the copy is stored on a single piece of media, since the disk itself could be destroyed.

So, yes: to be more careful, rotate two separate physical drives.

[Tom Lawrence]

If you're not rotating backups, then yes -- a power failure could destroy both the source and backup. This is true of non-clones as well as clones, if the copy is stored on a single piece of media, since the disk itself could be destroyed.

Thanks for getting back to me David. Swiss prices can sometimes be excessive so would appreciate a link to where you get your cables-they may work here.

Excuse my ignorance but how exactly do I rotate a back-up, other than to have two external drives?

[dnanian]

You could partition a drive into two volumes, but that wouldn't afford you the protection you're looking for.

Ah -- you're running 220V, which is different than the US voltage -- it's unlikely any UPS I pointed you to would work, alas...

[Tom Lawrence]

You could partition a drive into two volumes, but that wouldn't afford you the protection you're looking for.

Ah -- you're running 220V, which is different than the US voltage -- it's unlikely any UPS I pointed you to would work, alas...

:) Thanks anyway David. At least I now know again what a UPS is(been away too long....) and also i will take your advice and shop around. Should have gone the Computer Shop route in the first place rather than an electrician.

At the end of the day buying another external disk is also probably good value.

Not sure that partitioning is such a good idea these days but never say never.

One observation re using SuperDuper which I picked up from MacWizard on the MacFixit columns and which works well in practice for me: run DiskWarrior and Repair Permissions on the source before running SD; then run DW and RP on the clone before testing. Maybe it just gives you a nice warm feeling but, for what it is worth, DW has picked up some minor errors on the clone each time and then corrected them.

[dnanian]

Yes, the minor errors that DW finds on the copy are of basically no real consequence -- we've checked them with Alsoft a number of times. :)