margb

Q: Best way to connect multiple hard drives

Hi - Since getting my new Mac Pro, I have been working with two 12TB Promise Pegasus 2 Raid-5 hard drives.  They've been great.  But my video drive began getting scatty, and so I bought two WD-8TB backup drives, one to back up the key files on each PP2.  Sadly, it was too late to back up the video drive, as one of the bays was failing.  Because it's Raid-5, and thanks to the amazing and patient Venkat in Promise eSupport, I have replaced the failed drive bay, and am now waiting while it rebuilds itself with (hopefully without any data loss).  Then it will get backed up.

 

Until it became clear that a bad drive bay was probably underlying computer freezing, dropped frames in video playback, etc., I wondered if there was some sort of best practice for attaching external drives.  With Thunderbolt, you can daisy-chain; but what to what?  Is there a limit of some kind?  Should I connect the two Promise drives, then the closest one to the computer?  Should the WDs be connected the same way, each to each, and one to the computer?  Should there just be one four-drive daisy chain?   ????   In the old days, you had to watch how much power was being used when connecting USB and Firewire, but is the same true for Thunderbolt?

 

Surely would appreciate any insight into the best way to connect multiple hard drives.

 

Thanks!

Mac Pro, OS X Yosemite (10.10.1)

Posted on Jan 19, 2016 6:22 PM

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Q: Best way to connect multiple hard drives

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  • by Grant Bennet-Alder,

    Grant Bennet-Alder Grant Bennet-Alder Jan 19, 2016 8:13 PM in response to margb
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    Jan 19, 2016 8:13 PM in response to margb

    There are three unique Busses in the dark cylinder Mac Pro. Best responsiveness is with your drives distributed among the three busses, keeping in mind that Display Video takes nearly half a ThunderBolt Bus itself.

     

    You can use USB-3 for your Backup drives -- just keep in mind there is only enough bandwidth behind the USB to run one channel Reading and Writing full tilt. If you use more devices than that simultaneously, you may begin to see some clipping of your maximum transfer rate.

  • by margb,

    margb margb Jan 19, 2016 8:27 PM in response to Grant Bennet-Alder
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    Jan 19, 2016 8:27 PM in response to Grant Bennet-Alder

    Hi, Grant,

     

    Thank you so much for your reply. 

     

    The new WD backup drives don't have USB3, just Thunderbolt.

     

    How are the busses set up - that is, there are six Thunderbolt plugins, is each horizontal set of two connected to a separate bus, or is it some other configuration?  I'm just guessing that's the most logical setup ... would need to know that in order to attach drives in the right way.

     

    Once I know how the slots relate to the busses, I'm gathering that I could daisy-chain the Promise 12T drives on one slot on one bus, and daisy-chain the WD backups on a slot connected to a different bus.  The third bus can keep handling the video display (an older one that has both a USB and a Thunderbolt connection).  If I've understood you correctly, this should work best?

     

    I pretty much only use one Promise drive at a time - either I'm working on video or I'm working with non-video stuff on the other drive, and the backups only come into play when they do their backup thing.  Wish I could use Time Machine for both Promise drives, but it according to Apple it can only back up one drive.

     

    Very much looking forward to the clarification, and thanks again,

     

    Marg

  • by Grant Bennet-Alder,Solvedanswer

    Grant Bennet-Alder Grant Bennet-Alder Jan 19, 2016 8:41 PM in response to margb
    Level 9 (60,909 points)
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    Jan 19, 2016 8:41 PM in response to margb

    but it according to Apple it [Time machine] can only back up one drive

    I do not know where you got that idea, but it is not correct. Time Machine will back up all drives directly connected to your machine, unless you deliberately exclude some.

     

    This article shows which connector uses which Bus:

     

    Use multiple displays with your Mac Pro (Late 2013) - Apple Support


    .

  • by margb,

    margb margb Jan 19, 2016 8:50 PM in response to Grant Bennet-Alder
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    Jan 19, 2016 8:50 PM in response to Grant Bennet-Alder

    Hi, Grant,

     

    Thank you, the diagram was exactly what I needed.

     

    As to the Time Machine, you are right, but what I'd like to do is have it back up Promise A to WD A, and Promise B to WD B.  The dual setup - two independent backups - is what Apple Support said Time Machine couldn't do.

     

    I've clicked This solved my question and hope it takes.  I really appreciate your help and time.

     

    Marg

  • by Grant Bennet-Alder,

    Grant Bennet-Alder Grant Bennet-Alder Jan 20, 2016 7:14 AM in response to margb
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    Jan 20, 2016 7:14 AM in response to margb

    No it can't split them.

     

    But if you give it two destination drives, it will automatically alternate them, every other Backup session goes to every other drive, and each Backup drive is complete and independent of the other.

  • by margb,

    margb margb Jan 20, 2016 1:36 PM in response to Grant Bennet-Alder
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    Jan 20, 2016 1:36 PM in response to Grant Bennet-Alder

    That is very cool to know.  If I'm understanding you correctly, though, you still only have the capacity of one destination drive available at a time.  It's just unfortunate that I have so much to back up.  It takes judicious pruning to use an 8TB drive to back up a 12TB drive - only the fact that the 12TB is Raid5 and I keep 2 to 3 of the resulting 10TB as free space for better function, makes it possible.  There's sadly no way I could do a meaningful backup of both 12TB drives onto an 8TB machine, unless it knew where it stopped and would pick up from there the next time.  Now, if it could treat both 8TB drives as one, i.e. let the backed-up files overflow onto the second drive, that would actually do it!

     

    Thank you again for your help.

  • by Grant Bennet-Alder,

    Grant Bennet-Alder Grant Bennet-Alder Jan 20, 2016 8:07 PM in response to margb
    Level 9 (60,909 points)
    Desktops
    Jan 20, 2016 8:07 PM in response to margb

    That is called sometimes called "Just a Bunch Of Drives" JBOD RAID or Contented RAID. Up until the pulled the GUI for that out at ElCapitan, Disk Utility RAID could do that. The capability is still there, but now requires Terminal, or a multi-drive ThunderBolt or USB enclosure that can do it independently.

     

    In case you were wondering the Mac OS limit for drive size is something like 8 million TeraBytes, so you are nowhere near the limits.

  • by margb,

    margb margb Jan 21, 2016 6:16 PM in response to Grant Bennet-Alder
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    Jan 21, 2016 6:16 PM in response to Grant Bennet-Alder

    Hi, Grant,


    Again, thank you!  I'd found some references to JBOD online, but had the impression they were a poor choice, though the reason wasn't clear.  The WD drives can be configured in this way through their own software.

     

    Have been distracted by weird behaviour on the Promise drive that had to rebuild one of its bays, and by the fact that it kept coughing up warnings when I tried to use backup software to actually get a backup of that drive.  Today I gave up and reconfigured Time Machine to do just a backup of the video drive to its own WD drive, and that caused no problems at all, just six hours of sweating!  It may be clunky, but it makes more sense to spend five minutes setting up Time Machine for the alternate backups than to keep fussing with third party software that doesn't seem to play well with either Promise or WD.  Either that or the order of daisy-chaining has some impact - to do the TM backup today, I just plugged the WD into the Promise, and the Promise into the Mac itself, which I hadn't tried before.

     

    I've done some more research on JBOD since your response, and as far as reliability goes, I can't see that it's any worse than RAID 0 - in the sense that if one drive fails in either configuration, the data are toast.  Keeping the backup separated with multiple TM setups just ensures that if one backup drive fails, the other is unaffected.

     

    Your thoughts would be welcome, and thanks again so much.

     

    Marg

  • by Grant Bennet-Alder,

    Grant Bennet-Alder Grant Bennet-Alder Jan 22, 2016 7:55 AM in response to margb
    Level 9 (60,909 points)
    Desktops
    Jan 22, 2016 7:55 AM in response to margb

    The wireheads who are investing the time to understand RAID are usually motivated by the promise of massive performance or reliability improvements.

     

    Since JBOD provides no such improvement, it commands no respect. It is perfectly good at what it does, and there are no "gotchas" beyond what you have already observed -- that failure of a drive may cause you to lose all the data in the JBOD set. That is no surprise.

     

    Time Machine is not the absolute best backup software ever. Its "claim to fame" is that it is the Backup that gets done, because it works quietly in the background without you having to invoke it. When you have a crisis and need a Backup, your recent Time Machine Backup is more likely to be helpful than the truly excellent custom Backup you neglected to do this month, because it is such a pain.

  • by margb,

    margb margb Jan 23, 2016 2:36 PM in response to Grant Bennet-Alder
    Level 1 (0 points)
    Jan 23, 2016 2:36 PM in response to Grant Bennet-Alder

    Hi, Grant,

     

    The lack of trouble using Time Machine emboldened me to try Data Backup 3 again, in hope that it was the connection configuration that had caused the previous difficulty.  Although it took half again as long as TM to do the initial backup, it did complete with no error messages, and will do a daily versioned backup (Final Cut X backs up the video project files to the Mac computer directly, so the daily frequency on the video drive is acceptable).  And I was able to finish the first cut and burn a disk of the 2-hour Blu-ray video that I had been working on when all this kerfuffle started up.  Now I'm going to reconnect the other two disks in the same way as the video disk and its backup, and put TM back on that task.  May the Force be with all the darn disks!

     

    Your comments on JBOD's PR problem make perfect sense.  I am still thinking about doing a combined backup with that approach, but will wait to see how the parallel backups work out.

     

    Thank you for the help and support - drive configuration was a complete mystery to me before this.  Very much appreciated.