USB Hub and HD Configuration for backup

Posted on 2015-02-17
Medium Priority
Last Modified: 2016-11-23
I'm trying to get a particular backup set up to work.  This is in addition to 1) a local, always connected USB HD backup, 2) a remote offsite backup, and 3) an occasional physical offsite USB HD.  (Even the paranoid, etc.)

The goal of this *fourth* backup scheme is to have a daily rotation of a *disconnected* local backup.  The current approach is this:

> 3 USB portable HD's, each attached to a different switched port of a USB Hub,
> 3 incremental backup jobs, each aimed at one of the drive letters
>  the backup jobs would run every three days (except one, which would run two days in a row, because my backup SW is not that smart, and that's an acceptable "risk")
>  Each morning I would use the Hub switches to activate the HD that would "looked for" by the backup job that was going to run on that day, and to deactivate the other drives.

Currently, for the USB HD's, I have two WD2500ME's (WD 250 GB) and a WDBPGC5000ATT (WD Passport Ultra 500GB).  For the Hub I've currently got a Sabrient HB-UM43 (4 port, switched, unpowered).  The PC is a Dell XPS 8500.

The Hub is USB 3.0, the PC port is USB 3.0.  The 250GB's are USB 2.0, and the 500GB is USB 3.0.   The Hub is connected to the PC through its own 12" cable and a 6 foot USB 3.0 Extender.

The problem I'm running into is that when I "switch on" the 500GB, at the Hub, the PC recognizes it, after a couple of minutes.  But when I switch on the 250GB's the PC never recognizes them.  If the 250's are connected directly to the extender cable they work fine.

So, this could have several causes, and there might be several solutions.

I think the main cause must be that the 250GB's require more power than the 500GB, and that the link through the Hub cuts the power just enough that they don't hook up properly to the PC.

So, I could either get two more 500GB passports, or get a powered hub.   I'm tempted to get the passports, because I could use the 250's for the physical offsite backups, and they've served their time in any case.

So my "ask" here is four part:  
a) is there anything about this scheme that just "won't work", that I may not be considering?
b) is there some other reason the 250GB's might not be working through the Hub?
c) is a powered hub likely to help? (i.e. worth a try?)
d) what is a good quality powered 3.0 USB hub that has individually switched ports?  

Any help with this would be appreciated.

Question by:codequest
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Assisted Solution

by:Thomas Rush
Thomas Rush earned 2000 total points
ID: 40616200
The danger I see is that your backups are probably not independent, and so to do a restore, you'll need some of this media, then some of that, and maybe even some of a third... but you may not be able to get a consistent restore at all.

Here's why: a typical incremental backup job looks for files that have their archive bit set, backs them up, and resets the archive bit.  So, depending on which of your processes gets to a file first, a particular file could be in one of several places  -- but once job 'a' backs it up, it won't be backed up by job 'b' or 'c', unless it changes again, and then it's anybody's guess which of the jobs gets to back it up this time.

Better would be to use a differential backup, which doesn't reset the archive bit, so each backup process backs up every file changed since the last full backup (at the cost of some additional space used).  But you still have to go back to your last full backup to do a restore, and if you have two or more different applications doing full backups, you won't be capturing all the data and changes you think you are.

Best is to use one backup application only, set it to perform full + differential backups, and then make as many copies of those jobs' output to as many locations as makes you happy.

But to answer your question, yes, it's probably that you don't have enough power getting to the disks.  I'm sorry, but I don't have personal experience with switched powered USB hubs.

Author Comment

ID: 40617097
Thanks for the input.    I see the issue you point out.  Using Acronis (I should have said above)  I was thinking that if I had three separate incremental backup jobs pointed at three separate HDs, then each backup job would create a separate valid chain of incremental backups.  As each job came up, it would see only the appropriate HD, recognize the last incremental file in the chain, and then create the correct next incremental file, completely ignorant and independent of the other jobs.  So restore would depend only on that one media.  Does that explain it better, and do you still see a problem?

Thanks also for the input on the Hub.  There's one here:


however, I'm going to keep looking for one with a stronger brand.
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Expert Comment

by:Thomas Rush
ID: 40617113
I doubt that Acronis would work that way.  Take a look at http://www.acronis.com/en-us/support/documentation/ATIH2014/index.html#13711.html, which doesn't mention anything about being able to use independent disks -- but it does say specifically that an incremental backup "contains only those files which have been changed since the LAST BACKUP." (emphasis theirs)  Since your last backup would have gone to a different physical disk, and since to recover from a full+incremental backup set you need the full and *all* incrementals up to the desired recovery point, you're not gaining any additional safety or redundancy; in fact, you're probably introducing more failure points and potentially greater unreliability, since you'll need (often) all your rotating backup targets to allow you to complete a restore.

My recommendations:
1) Use Acronis exclusively if it provides the functionality you want; don't even think about using another backup application unless you fully understand how the two will interact with each other (not a trivial matter, and very likely to introduce unexpected and unwanted side effects).
2) Use full+differential backups to a single target to ensure the highest probability of restores
3) To meet your redundancy and off-site needs, once you have a full or differential backup complete, use Acronis (if supported) or your OS-level tools (robocopy, for instance) to copy the backup jobs to your desired secondary targets.

Accepted Solution

codequest earned 0 total points
ID: 40617257
Thanks for the input.  I looked up archive bit, which I did not understand.


However, it appears Acronis does not use the archive bit.


"Acronis Backup & Recovery 11 itself does not use the archive bit value. When performing incremental or differential backup, it determines whether a file has changed by the file size and the date/time when the file was last saved."

As reported by their support, SOS also does not set the archive bit, so there is no conflict with Acronis.   I've been using them together, and haven't had a problem.

I appreciate the robocopy idea;  Goodsync does that, and I use it to mirror my LAN drive to my local PC as the source for remote backup to SOS.  

I also appreciate the general input on this, it's made me have a much better understanding of these backup systems.  And I do like the idea of the differential backup vs incremental, for this "extra" non-attached backup.

I think I'll have to try out the multi-job Acronis approach, and see what happens.  I'll leave this open to post the result.

Assisted Solution

codequest earned 0 total points
ID: 40624908
Acronis forum says it should work;  I'm going to rely on that and close this question.

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Expert Comment

by:Thomas Rush
ID: 40625075
Glad you've gotten it to work, and that you got some useful knowledge out of the answers.

Author Closing Comment

ID: 40641366
My comment supplemented the information provided by the other commenter.
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