2021-05-15 ~21:00 BST (20:00Z) onwards forced reboot of host "jack"

Hi, Tonight from around 21:00 BST onwards we started getting alerts and support tickets regarding customer services on host jack.bitfolk.com. I had a look and unfortunately it appears to be a re-occurrence of previous issues regarding stalled IO: https://lists.bitfolk.com/lurker/message/20210425.071102.9d9a1cc5.en.html https://lists.bitfolk.com/lurker/message/20210220.032844.00dc9600.en.html https://lists.bitfolk.com/lurker/message/20201116.003514.25278824.en.html Things were largely unresponsive so I had to forcibly reboot the server. Customer services were all booted or in the process of booting by about 21:53. What we know so far: - It must be a software issue, not a hardware issue, as it's happened on multiple servers of different specifications. - It's only happening with servers that we've upgraded to Xen version 4.12.x. - It's going to be really difficult to track down because there can be months between occurrences. Each time this has occurred I've made some change that I'd hoped would lead to a solution, but I've now tried all the easy things and so all that remains is to do another software upgrade. I think we're going to have to build some packages for Xen 4.14 and install that on a test host and see how it goes. The difficulty is that once I do that and it seems to work, we'll never really know because it could just be in the long period of time where the problem is not triggered. Clearly once we have seemingly-working packages we can't leave them spinning for 6 months just to reassure ourselves of that. I also am unsure about whether it is a good idea to force additional downtimes on you in order to upgrade servers to 4.14.x when I don't even know yet if that will fix the issue. What I can do is have the upgrade ready and then if/when the issue re-occurs do the upgrade then, so it boots into that. Anyway, all I can say is that this is a really unfortunate state of affairs that obviously I'm not happy with and I'm doing all that I can to resolve it. These outages are unacceptable and rest assured they are aggravating me more than anyone else. Thanks, Andy Smith BitFolk Ltd -- https://bitfolk.com/ -- No-nonsense VPS hosting