USB3 on O3X

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USB3 on O3X

Postby xbytor » Mon Nov 17, 2014 1:22 pm

I've noticed people posting here that they are using USB3 enclosures with O3X. Did USB3 fix the problems the ZFS has with USB2 enclosures? Did I miss that memo?

-X
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Re: USB3 on O3X

Postby Brendon » Mon Nov 17, 2014 1:32 pm

There was no memo. The problems ZFS has with USB x.y.z is all about the quality of the controllers i.e. they may or may not exactly execute what ZFS believes them to have executed, leading to a somewhat weakened data integrity scenario. That's how I understand it anyway.

Many (most?) of our users appear to be USB 3 based, while some have reported poor performance, the majority have been silent, which we can only take as successful use.

Some users have had problems using USB because the drive device numbers can change based on reconfiguration of the devices attached to the USB bus. I believe an import/export or possibly reboot can resolve this.

- Brendon

xbytor wrote:I've noticed people posting here that they are using USB3 enclosures with O3X. Did USB3 fix the problems the ZFS has with USB2 enclosures? Did I miss that memo?

-X
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Re: USB3 on O3X

Postby DaveAbrahams » Sat Feb 07, 2015 5:29 pm

I did some experiments because I wanted to see how bad the data integrity issues were. In particular, these Seagate 2TB external drives are an awesome deal at $99, for my particular application: http://www.amazon.com/gp/product/B00FRHTTJE/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1 (mac mini ZFS server with low power consumption) — even if I end up throwing out the enclosures and just using the drives inside.

I bought four of them and filled the USB ports on my mac mini, created a stripe/mirror pool, and started 10 processes writing random data into separate files:

Code: Select all
for x in 0 1 2 3 4 5 6 7 8 9; do
  cat /dev/urandom > /tmp/random$x&
done


then I pulled the cables. A scrub revealed that basically every one of the files was corrupted. It's my understanding that if the enclosures were properly transmitting write barriers to the drives, there would have been no corruption. Some of the data that never reached the physical disk media would be lost, but none of the data that was written would have been altered.

My first inclination was to look for external enclosures that honor write barriers, but it's actually really hard to find any enclosures that promise to do so (presumably eSATA doesn't have this issue, but there's no eSATA on the mini). It seems the public at large is ignorant of the problem, so there's little incentive for vendors to worry about it. I'm not really worried that cables will be pulled or broken while the machine is running, but a similar problem can occur due to a power outage. The answer I came up with actually costs a lot less than most enclosures: a UPS. This one seems to do the job really well for a low price: http://www.amazon.com/gp/product/B00429N18S/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1.

I think I'll boot from an external USB drive, take two of the drives out of their enclosures and put them inside the mini where write barriers should be honored, and set ZFS as RAIDZ2. So even if the UPS fails, write barriers should protect the internal drives, which is enough to save all the data if nothing else goes wrong. That also leaves two USB ports free on the mini, which can be mighty handy.

In that configuration I'll try the test again, pulling the power cord on the mini, just to see if it makes a difference. I'll report the results here.

I'm still finding my way here a bit, so if you have any thoughts about this plan, I'd love to hear them.
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Re: USB3 on O3X

Postby MichaelNewbery » Sun Feb 08, 2015 5:45 pm

Over ten years ago, a colleague pointed out that of five incidents involving our UPS, in two of them the UPS had failed to provide uninterrupted power during a power failure; in two the UPS had failed (and interrupted power) when the mains power had not failed; and in only one had the UPS done its job --- an efficacy rating of a miserable 20%. At which point I was forced to agree with him that the cure was worse than the disease and abandoned the UPS. Also, such UPSs deliver horribly 'dirty' power which stresses many switching power supplies.

Note that there is a world of difference between that sort of individual unit and the big, generator backed systems used by service providers which do indeed supply clean power with impeccable reliability. Just such systems as my current employer uses. Said systems are not for sale on Amazon.

Things may have changed in the intervening years. Maybe.

As an aside, running the UPS at no more than 25% of nominal load helps (helped) immensely. (Whole building systems can sustain 100% load indefinitely and 110% load for an extended period of time.)
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Re: USB3 on O3X

Postby DaveAbrahams » Tue Feb 10, 2015 9:06 am

Well, if you believe these guys <https://www.youtube.com/watch?v=4QlF5vJlXaA>, this unit actually cleans up dirty wall power. This one seems to be way better than the Belkin I had ten years ago (which failed me, too, incidentally).

Anyway, combined with offsite backup, I think this is a pretty good setup.
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Re: USB3 on O3X

Postby westrock2000 » Mon Nov 09, 2015 3:25 pm

DaveAbrahams wrote:My first inclination was to look for external enclosures that honor write barriers, but it's actually really hard to find any enclosures that promise to do so (presumably eSATA doesn't have this issue, but there's no eSATA on the mini).


There are USB3 to eSATA adaptors. I do not know if any support Port Multiplication, which is important. You could always fill up a USB hub with eSata dongles :lol:

But there is also the possibility of buying a $200 Thunderbolt to PCI-e expansion box and then putting a $20 PCI-e eSATA card in it that has multiple ports as well as supporting port multiplication.
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Re: USB3 on O3X

Postby haer22 » Sun Nov 15, 2015 9:11 am

westrock2000 wrote:But there is also the possibility of buying a $200 Thunderbolt to PCI-e expansion box and then putting a $20 PCI-e eSATA card in it that has multiple ports as well as supporting port multiplication.

Or buy a TB2 box from Akitio (http://www.akitio.com/adapters/thunder2-dock ca $280) which has 2*eSATA (and USB3, FW800) and then run eSATA to 4bay enclosures.

I have two of those connecting my 4*4bay enclosures to my miniMac and I am a very happy camper.

I tried USB3 but the occasional renumbering just made life unbearable. That was before the InvariantDisks.
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