On Fri, 27 Feb 2026 20:52:51 +0000
Rainer Weikusat via Dng <dng@???> wrote:
> Copy of a message I also sent to 766@???
> ------------------------
>
> 1| mdadm: DeviceDisappeared event detected on md device /dev/md/md3
> 1| mdadm: DeviceDisappeared event detected on md device /dev/md/md2
> 1| mdadm: DeviceDisappeared event detected on md device /dev/md/md1
> 1| mdadm: DeviceDisappeared event detected on md device /dev/md/md0
> 2| mdadm: NewArray event detected on md device /dev/md0
> 2| mdadm: NewArray event detected on md device /dev/md1
> 2| mdadm: NewArray event detected on md device /dev/md3
> 2| mdadm: NewArray event detected on md device /dev/md2
>
> Short version: Won't happen anymore with 4.5, bug can be closed.
>
> Long Explanation:
> -----------------
> The 4.2 Monitor routine (in Monitor.c) uses the following loop to
> preprocess mdadm.conf entries:
>
> ,----
> | for (; mdlist; mdlist = mdlist->next) {
> | struct state *st;
> |
> | if (mdlist->devname == NULL)
> | continue;
> | if (strcasecmp(mdlist->devname, "<ignore>") == 0)
> | continue;
> | st = xcalloc(1, sizeof *st);
> | if (mdlist->devname[0] == '/')
> | st->devname = xstrdup(mdlist->devname);
> | else {
> | st->devname = xmalloc(8+strlen(mdlist->devname)+1);
> | strcat(strcpy(st->devname, "/dev/md/"),
> | mdlist->devname);
> | }
> |
> | [...]
> |
> | }
> `----
>
> This means it'll prefix array names which don't start with / with
> /dev/md. The so-qualified names will then be passed to the check_array
> routine:
>
> ,----
> | static int check_array(struct state *st, struct mdstat_ent *mdstat,
> | int test, struct alert_info *ainfo,
> | int increments, char *prefer)
> | {
> | /* Update the state 'st' to reflect any changes shown in mdstat,
> | * or found by directly examining the array, and return
> | * '1' if the array is degraded, or '0' if it is optimal (or dead).
> | */
> |
> | [...]
> |
> | char *dev = st->devname;
> |
> | [...]
> |
> | fd = open(dev, O_RDONLY);
> | if (fd < 0)
> | goto disappeared;
> |
> | [...]
> |
> | disappeared:
> | if (!st->err && !is_container)
> | alert("DeviceDisappeared", dev, NULL, ainfo);
> `----
>
> this will cause a single DeviceDisappeared alert if a name qualified in
> this way doesn't actually exist. This is responsible for the quoted
> output labelled with '1|' above.
>
> The lines labelled with '2|' were logged because the listed md devices
> weren't found in the /etc configuration but by scanning /proc/mdstat.
>
> In 4.5, the Monitor loop was changed to
>
> ,----
> | for (; mdlist; mdlist = mdlist->next) {
> | struct state *st;
> |
> | if (mdlist->devname == NULL)
> | continue;
> | if (is_devname_ignore(mdlist->devname) == true)
> | continue;
> |
> | st = xcalloc(1, sizeof *st);
> | snprintf(st->devname, sizeof(st->devname), "%s%s",
> | '/' == *mdlist->devname ? "" : DEV_MD_DIR, mdlist->devname);
> | if (!is_mddev(st->devname)) {
> | free(st);
> | continue;
> | }
> `----
>
> Among other things, is_mddev tries to open the qualified name and drops
> it from the list if this doesn't succeed. The names thus won't be passed
> to check_array anymore and won't cause alerts about disappearing devices
> anymore.
>
> The underlying issue must have been that a mdadm configuration file
> either contained the /dev/md/mdN¹ names or just the mdN names without a
> path.
Hi,
in my case /etc/mdadm.conf contained /dev/md0 as name
because mdadm 4.4-11devuan3 itself created it that way
(or maybe I created this array with that dev name,
could this be the cause? should I have used /dev/md/0?).
There must have been some other weird interaction with eudev
or some other corner case I was not able to detect.
Hope this is fixed in 4.5 as you said.
I still wonder why we have started to play this games
with device names that worked for decades.
What is the difference in having /dev/md0
or /dev/md/0 in /dev? What is the advantage
of this name change? I don't see any...
the kernel, if I understand correctly
the meaning of the %k substitution var
for udev rules, still proposes md0 as device name.
Thanks for your time and effort.
Ciao,
Tito
> ¹ By default, /dev/md contains symlinks of the form /dev/md/N ->
> /dev/mdN which are created by a udev rule on aray detection.
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::
Re: [DNG] Regarding mdadm bug 766
