On 01/24/2018 06:36 PM, Linus Lüssing wrote:
Hi,
Many thanks for all the quick and helpful responses so far!
On Tue, Jan 23, 2018 at 06:40:14PM -0600, Stan Hoeppner wrote:
Could someone elaborate further on this? Does "interacts very
badly" mean that there will be potential data loss / data
corruption? Or does "very badly" just mean short, temporary
performance issues / lags upon a disk failure?
Potential data loss / data corruption. Don't use USB. Use eSATA instead.
The list archives of linux-raid and linux-xfs are dotted with USB disk
horror stories.
Interesting. Do you know what they could be attributed to
technically? Were they usually similar to what Vojtěch had
described, so connectivity issues due to the poor connectors and
thin cables which can often be found with USB? And things then
fell over when for a brief moment connectivity issues occured for
more disks than redundant disks were configured? Or do the extra
latencies with USB create an extended exposure to the write loop
hole in RAID5? Or something else?
Here is an example of what you may see with a USB connected drive:
http://forums.debian.net/viewtopic.php?f=10&t=48056
You'll have to read up on the USB protocol to see why devices are
reset. As with the user in this post, your USB connected drive may
function fine for a while, but on occasion you'll hit one of these reset
conditions. When that occurs your filesystem may survive, or you may
suffer corruption, or data loss. I for one would not rely on storage
that is reliable only 99% of the time. Murphy's law dictates it will
fail at the worst possible time.
Would you guys say that ARM boards with a SATA connector
internally weird to USB (for instance the Ordoid HC2[*]), and then
maybe some SATA Port Multiplier are similarly affected? Or would say
that those are mainly unaffected of the common issues with RAIDs
via SATA over USB?
Regards, Linus
[*]: http://www.hardkernel.com/main/products/prdt_info.php?g_code=G151505170472&tab_idx=2
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