danseq
Level 2 (155 points)

Q: is there an upper limit to the number of drives that can be connected?

So I'm on a 2010 6-core 3.33ghz

5,1 model

32GB ram

Currently on 10.10.5, but this problem was also on Mavericks.

 

I do audio production and thus need a lot of drives running simultaneously.

 

I have (internal SATA):

 

-2TB SSD as boot

-1TB SSD

-2TB HD

-1TB HD

-600GB HD

 

Then I have a FASTA-6GU3 Pro - eSATA 6G and USB 3.0 Combo Card

Between that and the built-in FW and USB ports I am servicing 4 docks of various brands and interfaces (some of them dual) containing:

 

-500GB SSD

-1GB HD

-8TB Seagate archival drive

-8TB Seagate archival drive

 

I use both the 8TB drives as my time machine (staggered). The problem is, I rarely can get both to mount simultaneously, but when I do get them both to mount, one of the internal drives usually gets booted off the bus. I have this feeling I'm exceeding some sort of limit in a zero-sum situation.

 

I have tried many different combinations of USB, FW800, and eSata, using internal bus, external ports, and card‚—mixing things and trying to distribute things across different kinds of busses. Putting both 8tb drives in a new dock (which claims to be able to house 2x8TB), and putting them in separate docks. But always having the issue that I can't get all 9 drives online simultaneously except on rare occasion. Once a drive is kicked off the bus, only a restart can get it back.

 

I guess what I'm wondering is whether there is an upper limit to the number of storage devices that can be online at once, or is there an upper TB limit?

 

Any insights into this would be appreciated. Thanks!

Mac Pro, OS X Mavericks (10.9.2), 5,1 6-core 3.33Ghz, 32GB RAM

Posted on Oct 14, 2015 2:55 PM

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danseq

Q: is there an upper limit to the number of drives that can be connected?

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  • by danseq,

    danseq danseq Oct 14, 2015 3:38 PM in response to danseq
    Level 2 (155 points)
    Oct 14, 2015 3:38 PM in response to danseq

    one of my internals is 3TB, not 1TB, but the point is, the internals have been fine for months. The problem really started happening when I added a 2nd 8TB drive to my externals.

  • by BDAqua,

    BDAqua BDAqua Oct 14, 2015 4:04 PM in response to danseq
    Level 10 (123,905 points)
    Oct 14, 2015 4:04 PM in response to danseq

    Hi, that shouldn't be too many drives with your setup, each bus has it's limits, but you're not even close FW & USB, though power can be an issue, how many of the externals are Bus powered?

     

    I suspect either drivers or the most recent drives, or power issue.

  • by danseq,

    danseq danseq Oct 14, 2015 4:20 PM in response to BDAqua
    Level 2 (155 points)
    Oct 14, 2015 4:20 PM in response to BDAqua

    Thanks BDAqua,

     

    None of the externals are bus powered. I use four powered docks, each with its own wall wart.

    Some docks do have an 8tb limit, but even with each drive in a separate dock I have the issue.

  • by danseq,

    danseq danseq Oct 14, 2015 5:18 PM in response to danseq
    Level 2 (155 points)
    Oct 14, 2015 5:18 PM in response to danseq

    Someone mentioned to me that there have been reports of problems when 8TB is exceeded on the internal SATA bus. Since I was just over that limit, I swapped the internal 3TB HD for a 500GB SSD, dropping the internal storage well below 8TB and restarted. This did not change the total amount of drives or storage--just moved things around. After a reboot, for just a few minutes I had all drives up, but alas, after about 10 minutes or so, one of the drives (the 3TB I had moved to a dock) was kicked off the bus.

     

    No such luck. This is really weird.

  • by BDAqua,Helpful

    BDAqua BDAqua Oct 14, 2015 6:24 PM in response to danseq
    Level 10 (123,905 points)
    Oct 14, 2015 6:24 PM in response to danseq

    Yes, some Docks have a far lower limit too, but that isn't what I thought you were asking, I thought it was pure number of drives the OS could handle overall.

     

    After rereading your post, it may very well be that though natively handled, OSX may be confused, or as often happens it comes down to who is interpreting the "Standards".

     

    Any chance you could have over 2 billion files & folders when they're all connected?

     

    Mac OS X: Mac OS Extended format (HFS Plus) volume and file limits - Apple Support

  • by danseq,

    danseq danseq Oct 14, 2015 6:24 PM in response to BDAqua
    Level 2 (155 points)
    Oct 14, 2015 6:24 PM in response to BDAqua

    Nope, a quick estimate is between 15-20 million files/folders total.

     

    I thought also it might be the PCIe card, because I have had some reports of the card getting flaky when more than two of its 4 ports (2 USB3, 2 eSata) are used, but I've had an hour of stability taking all drives off of the built-in USB bus and putting everything else on either the card, or built-in FW. I'm not drawing any conclusions yet, because all of the temporary solutions that I thought would work turned out to be flaky and I don't expect this to last.

     

    But if I get a single productive evening of a few hours without any more drives being kicked off, then I'll assume I've found some configuration that may work. Maybe I have too many external USB devices (I have a lot), and that's what's bothering my system.

  • by BDAqua,Helpful

    BDAqua BDAqua Oct 16, 2015 3:18 PM in response to danseq
    Level 10 (123,905 points)
    Oct 16, 2015 3:18 PM in response to danseq

    I wonder if one or more of the PSUs for the USB drives is/are dead & running off of B us Power?

    USB hubs could be cascaded up to seven levels deep, however maximum number of user devices is reduced by number of hubs. With 50 hubs attached, the maximum number is 127 − 50 = 77

    https://en.wikipedia.org/wiki/USB_hub

  • by danseq,

    danseq danseq Oct 16, 2015 3:33 PM in response to BDAqua
    Level 2 (155 points)
    Oct 16, 2015 3:33 PM in response to BDAqua

    Since my last post I haven't had any drives booted off the machine during normal operation. Everything is working since eliminating any hard drives being on the USB2 built-in bus. It isn't that I have anywhere close to the number of devices listed in the article as a limitation, but there are enough nested hubs and other devices (including a display link 17" monitor) that I think there's a bandwidth issue or something. Not sure about power although loss of a power adapter in back of my desk is possible. I haven't checked that. The only other thing I haven't checked is swapping docks, so it is possible that the dock I'm using on that bus is faulty in some way. Will test that scenario out eventually.

     

    What nags at me a little though is that many times it was NOT the drive connected via USB2 that was being dismounted. Sometimes it was an internal SATA, or sometimes a dock attached to my PCIe card. So I have to surmise that the drives are being looked at in some kind of gestalt, and the OS makes it's own decisions about what to boot off when things get squirrelly even on another bus.

     

    Thanks for the ideas!

  • by BDAqua,

    BDAqua BDAqua Oct 16, 2015 4:07 PM in response to danseq
    Level 10 (123,905 points)
    Oct 16, 2015 4:07 PM in response to danseq

    Good work, thanks for the report… does seem like some power issue affecting the OS.