On Fri, Dec 8, 2023 at 3:15 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > On Fri, Dec 08, 2023 at 02:49:39PM +0800, Yafang Shao wrote: > > On Fri, Dec 8, 2023 at 1:36 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > On Thu, Dec 07, 2023 at 08:36:56PM +0800, Yafang Shao wrote: > > > > On Thu, Dec 7, 2023 at 8:12 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > On Thu, Dec 07, 2023 at 07:59:03PM +0800, Yafang Shao wrote: > > > > > > On Thu, Dec 7, 2023 at 6:19 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > > > On Wed, Dec 06, 2023 at 10:08:40PM +0800, Yafang Shao wrote: > > > > > > > > On Wed, Dec 6, 2023 at 9:31 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > > > > > > > > On Wed, Dec 06, 2023 at 11:53:55AM +0000, Yafang Shao wrote: > > > > > > > > > > After upgrading our kernel from version 4.19 to 6.1, certain regressions > > > > > > > > > > occurred due to the driver's asynchronous probe behavior. Specifically, > > > > > > > > > > the SCSI driver transitioned to an asynchronous probe by default, resulting > > > > > > > > > > in a non-fixed root disk behavior. In the prior 4.19 kernel, the root disk > > > > > > > > > > was consistently identified as /dev/sda. However, with kernel 6.1, the root > > > > > > > > > > disk can be any of /dev/sdX, leading to issues for applications reliant on > > > > > > > > > > /dev/sda, notably impacting monitoring systems monitoring the root disk. > > > > > > > > > > > > > > > > > > Device names are never guaranteed to be stable, ALWAYS use a persistant > > > > > > > > > names like a filesystem label or other ways. Look at /dev/disk/ for the > > > > > > > > > needed ways to do this properly. > > > > > > > > > > > > > > > > The root disk is typically identified as /dev/sda or /dev/vda, right? > > > > > > > > > > > > > > Depends on your system. It can also be identified, in the proper way, > > > > > > > as /dev/disk/by-uuid/eef0abc1-4039-4c3f-a123-81fc99999993 if you want > > > > > > > (note, fake uuid, use your own disk uuid please.) > > > > > > > > > > > > > > Why not do that? That's the most stable and recommended way of doing > > > > > > > things. > > > > > > > > > > > > Adapting to this change isn't straightforward, especially for a large > > > > > > fleet of servers. Our monitoring system needs to accommodate and > > > > > > adjust accordingly. > > > > > > > > > > Agreed, that can be rough. But as this is an issue that was caused by a > > > > > scsi core change, perhaps the scsi developers can describe why it's ok. > > > > > > > > > > But really, device naming has ALWAYS been known to not be > > > > > deterministic, which is why Pat and I did all the driver core work 20+ > > > > > years ago so that you have the ability to properly name your devices in > > > > > a way that is deterministic. Using the kernel name like sda is NOT > > > > > using that functionality, so while it has been nice to see that it has > > > > > been stable for you for a while, you are playing with fire here and will > > > > > get burned one day when the firmware in your devices decide to change > > > > > response times. > > > > > > > > I agree that using UUID is a better approach. However, it's worth > > > > noting that the widely used IO monitoring tool 'iostat' faces > > > > challenges when working with UUIDs. This indicates that there's a > > > > significant amount of work ahead of us in this aspect. > > > > > > That indicates that iostat needs to be fixed as this has been an option > > > that people rely on for 20+ years now. Or use a better tool :) > > > > The issue arises when a disk contains multiple partitions, such as > > /dev/sda1 and /dev/sda2. In this case, using 'iostat -j UUID' can only > > display 'sda' since only its partitions possess UUIDs. Uncertain how > > to address it yet. > > Then use one of the other many other unique ids that are in /dev/disk/ > today. You have loads of things to choose from: > $ ls /dev/disk/ > by-diskseq by-id by-label by-partlabel by-partuuid by-path by-uuid > > You have a plethera of choices here, use whatever works best for your > systems. This is a userspace decision to make, not a kernel one, as > this is a policy choice of yours. > Indeed, there are alternative methods besides using UUIDs. This example serves to highlight that UUIDs might not cover all scenarios, similar to other IDs listed under /dev/disk/. -- Regards Yafang
