USB 3.0 test results (spoiler: not so good)

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USB 3.0 test results (spoiler: not so good)

Post by ferebee » Mon Apr 29, 2013 7:25 am

As detailed in another post http://zevo.getgreenbytes.com/forum/viewtopic.php?f=4&t=1649 I've been looking at creating raidz volumes with USB 3.0 hard drives. Of the available USB 3.0 hubs, the Genesys Logic GL3520 chipset seems like the best bet, and I've obtained a 7-port EXSYS EX-1188HMS hub that uses it.

At first I had problems getting my assorted USB 3.0 drives (3 TB Seagate ST3000DM001-9YN166 with JMicron and VIA USB-SATA bridge controllers) to connect at USB 3.0 SuperSpeed. Instead, they would show up as HighSpeed (USB 2.0) devices. After disconnecting my assorted other USB 2.0 hubs and devices, that problem went away, at least.

Using 4 drives, all connected to the hub, I created a new raidz volume, and ran multiple simultaneous rsync copies to it, transferring 3 TB in total, from the Mac mini's internal SSD, internal HD, two external FireWire drives and a different USB 3.0 drive also connected to the hub. Things appeared to go well, with zpool iostat reporting write rates of between 80 and 130 MB/s and between 1.000 and 10.000 write IOPS.

However, as a test, I also connected my iPhone to the hub. It seemed to charge properly and was recognized by iTunes, but several times during the test it played the "USB connected" chime. I suspect that the USB connection was interrupted and/or the bus reset for some reason.

I also started a zpool scrub about halfway through the test. It's almost done, and shows errors:

Code: Select all
  pool: zusb
 state: ONLINE
status: One or more devices has experienced an unrecoverable error.  An
   attempt was made to correct the error.  Applications are unaffected.
action: Determine if the device needs to be replaced, and clear the errors
   using 'zpool clear' or replace the device with 'zpool replace'.
 scan: scrub in progress since Sun Apr 28 10:55:40 2013
    3,78Ti scanned out of 3,85Ti at 41,9Mi/s, 0h26m to go
    176Ki repaired, 98,38% done
config:

   NAME                                           STATE     READ WRITE CKSUM
   zusb                                           ONLINE       0     0     0
     raidz1-0                                     ONLINE       0     0     0
       GPTE_EEE87000-C79D-47E7-8A38-AF4F5784EEC6  ONLINE       0     0     2  at disk7s2  (repairing)
       GPTE_EA19AF8A-C371-4016-9BF1-253664AB3363  ONLINE       0     0     1  at disk8s2  (repairing)
       GPTE_311D11BB-4CFE-4A7F-B734-C693E48DE7EA  ONLINE       0     0     0  at disk9s2
       GPTE_0C7D2F0F-A79B-464F-9F90-BB9720197974  ONLINE       0     0     1  at disk10s2  (repairing)


I don't know what caused these errors, but I draw two conclusions:

1. Current no-name USB 3.0 hard drives, connected through a GL3520 hub, running under OS X 10.8.3, are not reliable.

2. There is a very good reason ZFS checksums everything. Fear HFS+, especially over USB 3.0.
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Re: USB 3.0 test results (spoiler: not so good)

Post by ilovezfs » Mon Apr 29, 2013 8:01 am

This is very disappointing. When the scrub finished, did it report any outstanding data errors? You might want to look at this thread for some examples of scrub output when data errors remain even after scrub: viewtopic.php?f=4&t=2034

I think some transient errors have to be expected given that USB devices will inevitably disconnect when you don't want them to at some point. If ZFS recovers easily from such fleeting errors caused by temporary disconnection, I think your tests may have been more successful than you think, assuming there are no data errors at this point.

176Ki repaired out of 3.78Ti doesn't sound like it disqualifies this setup at all, especially if zpool status and zpool status -v aren't reporting any errors after scrubbing.
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Re: USB 3.0 test results (spoiler: not so good)

Post by ferebee » Fri May 03, 2013 6:48 am

The scrub took a long time to finish and stayed at "101.4% done" for hours. In the end, it did complete sucessfully, I cleared the errors and things appeared to work normally for a while.

A day or two later, I found myself unable to access the pool anymore, the Finder, Disk Utility and other apps were stuck, and I had to force a shutdown of the Mac.

After rebooting, it turned out that of the five USB 3.0 drives connected to the Mac, the two that use a VIA USB-to-SATA bridge (USB product ID 0x0701, vendor ID 0x2109, version 3.0.7, marketed as "Intenso Memory Box 3 TB") had gone offline. I had to power-cycle the drives to bring them back. ZFS then resilvered the pool:

Code: Select all
 scan: resilvered 35,3Mi in 0h0m with 0 errors on Fri May  3 12:27:59 2013


While both drives with VIA controllers crashed, the other drives stayed online, two with JMicron controllers and one on a Seagate GoFlex Desk adapter.

I am now inclined to distrust VIA USB bridge boards as much as I distrust VIA USB hubs.
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Re: USB 3.0 test results (spoiler: not so good)

Post by ilovezfs » Fri May 03, 2013 7:06 am

ferebee wrote:A day or two later, I found myself unable to access the pool anymore, the Finder, Disk Utility and other apps were stuck, and I had to force a shutdown of the Mac.

Just as a point of reference for you, I have encountered the same symptoms occasionally while using ZEVO, so this may not have had anything to do with your using a hub. They usually seem to be associated with some dismount/detach not succeeding, which then leads to some sort of deadlock.

I am glad to hear your scrubs and resilvers are finishing error free.
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Re: USB 3.0 test results (spoiler: not so good)

Post by ferebee » Fri May 03, 2013 6:18 pm

I don't think the hub is at fault at all. The Genesys Logic GL3520 seems to be performing flawlessly AFAICS, as in "there are always some USB 3.0 devices connected to the hub that are operating correctly".

I blame everything else. USB 3.0 seems to be a very immature technology. Does anybody test this stuff? I can see why Apple took so long to ship it.

My final conclusion is: the only way to use USB 3.0 is with ZFS. A filesystem that doesn't do end-to-end checksumming is doomed if it's deployed over USB 3.0. Yes, so far all the scrubs have completed and repaired all errors.
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Re: USB 3.0 test results (spoiler: not so good)

Post by ilovezfs » Fri May 03, 2013 6:37 pm

If you're still planning on getting the 2011 iMac, any reason for not just using Thunderbolt drives instead of Belkin + USB 3.0 Hub?
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Issues with Intenso Memory Box 3 TB (0x0701)

Post by grahamperrin » Sat May 04, 2013 2:26 pm

freebee wrote:… two that use a VIA USB-to-SATA bridge (USB product ID 0x0701, vendor ID 0x2109, version 3.0.7, marketed as "Intenso Memory Box 3 TB") had gone offline. I had to power-cycle the drives to bring them back. …


Nothing Mac-specific amongst the downloads at http://www.intenso.de/downloads_en.php? ... 1323328654

If the hardware goes offline in a way that's problematic, try disallowing sleep of hard disks in the Energy Saver pane of System Preferences. That could be a workaround, but not a solution.

Also or alternatively: Keep Drive Spinning
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Re: USB 3.0 test results (spoiler: not so good)

Post by ferebee » Tue May 07, 2013 4:37 am

@grahamperrin I would never install software from a no-name hard drive vendor. I think you have had your share of poor experiences even with name-brand driver software. :-)

As for spindown issues - in my opinion, a drive that is unable to spin down and up correctly is a defective design. (It seems you agree.) At the moment, I have 9 drives of various types connected to the Mac mini over FireWire, USB 2.0 and USB 3.0, using HFS+ and ZFS, and they all do spin down and up correctly.

The two drives with the VIA bridge controller didn't just spin down, they went completely offline, i. e. were no longer visible on the USB, even after power cycling the Mac and the USB hub. That's why I think the bridge controllers crashed hard.

These days, 3 TB USB 3.0 drives tend to be cheaper than bare 3 TB SATA drives, and almost all of the USB drives have come with Seagate Barracuda 7200.14 mechanisms, which appear to work fine as bare drives in NAS and other server applications. (No issues so far with excessive head parking etc.) I just buy whatever USB drives are on sale, and test to see whether they work properly. It seems to be pot luck what sort of bridge controller you get. The enclosures that don't work get their drives pulled and chucked.

Not an ideal situation, but with the current state of USB 3.0 I don't know a better way.
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