video stuttering

Hey, remember my video stuttering problem? Well, when I boot off of my backup drive, videos play fine. Great.

Both the internal and external drive are about a month old, bought at the same time. HGST Deskstar 4TB 7200 RPM SATA III 6Gbps, 64MB Cache. External drive is in a FW800 enclosure.

So what could possibly have gone wrong here?

I guess I could pull the machine apart again and swap the two drives. I'm not sure what else to try.

It seems very unlikely to me that one of these drives is faulty when the other is not, especially as it doesn't seem to exhibit any other failures (nothing in logs, I/O seems fast, etc.)

But even if it's a motherboard problem that just happened to manifest when I swapped drives, it is still an I/O problem so why can't I prove that with numbers?

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Current Music: Ms Mr -- No Trace ♬

32 Responses:

  1. Kevin Lyda says:

    It wouldn't be surprising for one of two drives to fail early. These guys have experience with lots and lots of hard drives and have kept stats on their experiences.

    That said, when you boot off the backup drive, is it on a different bus? Seems to be - external is firewire, internal is sata. Bad sata cable? Or maybe it's getting too hot inside the computer?

  2. Emily says:

    Backing up what Kevin says, I had a Macbook Pro where the internal HDD failed three times in a year (each time it was losing data). Turns out it was the SATA cable (which is a pain to replace on the Mid-2009 Macbook Pros). We worked this out by using Scannerz ( on the drive connected to the internal SATA and then again via USB. From reading comments since then, it seems that this is an emerging problem on Macbook Pros...

    • jwz says:

      Well, it's the same internal cable that was in there before. I'm reasonably sure I seated it properly, though, because this is not my first rodeo. (If only it didn't take over an hour to disassemble and reassemble iMacs...)

      • Emily says:

        This was the page that helped me... Maybe it has some info which could help you.

      • Charles says:

        SATA cables aren't spec'd for a huge number of removal/reinsertion cycles, and the cables can develop intermittent problems from other causes -- exceeding the bend radius while fiddling with them, etc. They go "bad" sooner and more often than you might expect.

        Swapping the cable is a pain, but probably slightly less painful than swapping the drive. 10:1 a new cable fixes it.


        • Tim says:

          SATA uses CRC to detect when packets didn't make it across the wire OK. SATA drives will report these CRC errors as one of the SMART statistics (the one named "UDMA_CRC_Error_Count" -- if you're wondering why "UDMA", it's because the feature was first introduced on UltraDMA parallel ATA, and they never changed the name).

          jwz's drive is reporting zero CRC errors. It's probably not the cable.

          • Charles says:

            Unless I'm very much mistaken, the drive's SMART stats will only report packets received at the drive with failed CRCs. It won't capture packets that were corrupted arriving at the SATA controller -- and since those go over a different pair of conductors, it's entirely possible the cable is intermittently flaky in only one of the two directions. The resulting required retransmits would explain the stuttering.

            It may or may not be the cable -- but the cable is definitely the first thing I would try swapping.

            • jwz says:

              Do you happen to know what kind of cable is required for a mid-2010 iMac11,3 with a 4TB SATA3 drive? I assume SATA cables are not all the same, and I'm having a hard time googling up that answer.

              • Charles says:

                Actually, all "normal" SATA cables for 2.5" and 3.5" drives (i.e. not SATA-e, or SFF8087-to-SATA breakout cables, or other oddities you won't find inside your Mac) are the same; the only technical differences are whether they have a locking clip or not, and whether they have straight or right-angle connectors. I've not seen the inside of your Mac, but get the same end configuration as you currently have. All cables made in the last few years should be fine for SATA3 (6Gbps) use, but I'd avoid the absolute cheapest yum-cha cables.

                If you have a local computer hardware parts place you like, whatever they have in their house brand is likely to be okay. If you'd prefer to mailorder, any of Monoprice's cables are fine as long as they meet your length requirements. Don't get one that's a foot longer than you need. These, depending on length and quantity, are in the $2-3 range.

                • jwz says:

                  Well that was fun.

                  I swapped the backup drive into the machine: still skips! So it's not the drive.

                  I was gonna replace the cable, but the other end disappeared under a board that I couldn't figure out how to remove.


                  • Charles says:

                    The problem not following the drive is good info; after eliminating the drive, it is much more likely to be the cable than the SATA controller port on the mainboard. It could also be a driver problem but I don't know offhand if the Intel MB SATA drivers changed in your OS point-release upgrade.

                    Regarding getting at that cable... I don't actually know what "Imac 11,3" as a model number means, so I don't know the exact machine you're referring to.

                    Would you be so lucky that it's one of the Imac models listed in the teardown/repair guides at Ifixit?

            • Tim says:

              Re: the bidirectionality of the SMART statistics, I don't have the relevant standards in front of me so I can't say definitively. But I'm fairly sure SATA retries bad packets, which requires some sort of ACK/NAK scheme, which means that the drive should know when packets it sends aren't received correctly.

  3. Tim says:

    Got smartmontools installed? If so, what's smartctl -A /dev/disk0 say?

    • jwz says:

      It says... stuff...

       1 Raw_Read_Error_Rate     0x000b   100   100   016    Pre-fail  Always       -       0
       2 Throughput_Performance  0x0005   136   136   054    Pre-fail  Offline      -       80
       3 Spin_Up_Time            0x0007   168   168   024    Pre-fail  Always       -       485 (Average 436)
       4 Start_Stop_Count        0x0012   100   100   000    Old_age   Always       -       18
       5 Reallocated_Sector_Ct   0x0033   100   100   005    Pre-fail  Always       -       0
       7 Seek_Error_Rate         0x000b   100   100   067    Pre-fail  Always       -       0
       8 Seek_Time_Performance   0x0005   100   100   020    Pre-fail  Offline      -       0
       9 Power_On_Hours          0x0012   100   100   000    Old_age   Always       -       940
      10 Spin_Retry_Count        0x0013   100   100   060    Pre-fail  Always       -       0
      12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       8
      192 Power-Off_Retract_Count 0x0032   100   100   000    Old_age   Always       -       54
      193 Load_Cycle_Count        0x0012   100   100   000    Old_age   Always       -       54
      194 Temperature_Celsius     0x0002   115   115   000    Old_age   Always       -       52 (Min/Max 21/54)
      196 Reallocated_Event_Count 0x0032   100   100   000    Old_age   Always       -       0
      197 Current_Pending_Sector  0x0022   100   100   000    Old_age   Always       -       0
      198 Offline_Uncorrectable   0x0008   100   100   000    Old_age   Offline      -       0
      199 UDMA_CRC_Error_Count    0x000a   200   200   000    Old_age   Always       -       0

      • phuzz says:

        As far as I can tell, most of that llooks fine, but the temperature at 52 degrees (ID# 194) is at the upper end of what's safe for a harddrive (although the manufacturer specs say 60).
        I'm afraid the next course of action is probably to try the backup drive plugged-in internally so you can narrow it down to either the disk or the interface.

      • Tim says:

        According to the RAW_VALUE colum you have zero reallocated sectors (ID #5 Reallocated_Sector_Ct, #196 Reallocated_Event_Count), and there are zero sectors in the middle of going bad or being spared out (if there were you'd expect #197 or #198 to be greater than 0). Additionally, zero CRC errors (#199) means that you probably do not have a bad cable.

        So there's nothing from the SMART report suggesting the usual reasons why drives might time out for a while, which would've explained your video stuttering. On the other hand at least it looks like the disk is healthy...

  4. Rodger says:

    It's not CoolSpin branded is it? I've seen a buttload of complaints about those spinning down every 30 - 90 seconds, then having to spin up again.

  5. nooj says:

    All this st-stuttering b-business seems to be holding up a much-ancitipated mixtape. So, here are some bands I've enjoyed:

    Prides, "Out of the Blue":

    Zella Day, "Sweet Ophelia":

    Jungle, "Busy Earnin'":

    The Twoks ("twahks", not "tooks"), "240 Volts":

  6. waitwhat says:

    > Unfortunately, a bunch of things have changed on this machine over the last few months, and I'm not sure exactly when this problem began: I've upgraded from 10.9.1 to 10.9.2; replaced the RAM; replaced the internal drive. So there are several things that could have been the cause. It could be some new stupidity in the Quicktime library, or a disk performance problem, or... well, maybe it can only be those two.

    This sounds very familiar - I had those symptoms AND I had display corruption on my iMac that I could only reproduce occasionally. Apple store tested it for 24 hours (their claim) and found nothing wrong. Got tired and sold that piece of crap. So much for it just works.

    I think you might want to try putting in a SSD in place of that drive - given most of Apple's hardware now ships with SSD - may be they stopped caring about the rotating drives.

  7. Andre Stechert says:

    Perhaps when booting from the external drive, the OS begins using the external driving for logging, swap, etc., reducing I/O contention. Does the stuttering always stop when the video is on a different spindle from the booted partition?

    • jwz says:

      I meant: both booted off of and playing videos off of the external drive. Internal drive not mounted.

  8. Grey Hodge says:

    You know, an idea for trouble shooting which you may very well hate would be to swap out another drive and install another OS, like Windows or Linux JUST FOR TESTING, then try to stress the IO on both the internal port and the external port. If all goes perfectly smoothly, then MacOS is not configuring or using the internal SATA port right suddenly, and you at least have something to look at. If it gives the same or similar issue, you know it's the mobo. I know I know, you hate MS and Linux is for the BDSM crowd, but I only suggest it for testing, so, like, a couple hours tops.