Hello,

On 11/19/20 10:21 AM, Jorge Fábregas wrote:

On 11/18/20 12:45 PM, heming.zhao@suse.com wrote:

quoted

The events is related with (struct mddev) mddev->events.
you can search it in kernel source code.

Thank you Heming.  I was expecting more of a general view since I'm a
new user.  Sorry I wasn't clear.

very general overview: if array status/superblock is changed, event will increase.

What sort of events cause the Event counter to increase?  If it's mainly
whenever the superblock is updated then my question is: What sort of
events cause the superblock to be updated? I can imagine detection of
failed disk, read errors, array checks, commands by user/admin,
assembly-reassembly etc? If an array operates fine for months - without
user intervention,  will the Event counter increase at all?

the status/event is the content of struct mdp_superblock_1:
    __le64  ctime;      /* lo 40 bits are seconds, top 24 are microseconds or 0*/
    __le32  level;      /* -4 (multipath), -1 (linear), 0,1,4,5 */
    __le32  layout;     /* only for raid5 and raid10 currently */
    __le64  size;       /* used size of component devices, in 512byte sectors */

    __le32  chunksize;  /* in 512byte sectors */
    __le32  raid_disks;
    ... ...
    __le64  reshape_position;   /* next address in array-space for reshape */
    __le32  delta_disks;    /* change in number of raid_disks       */
    __le32  new_layout; /* new layout                   */
    ... ...
    __le32  dev_number; /* permanent identifier of this  device - not role in raid */
    ... ...
    __le16  dev_roles[0];   /* role in array, or 0xffff for a spare, or 0xfffe for faulty */ 

I am not very familiar with md, and can't enumerate all the cases. For your writing:
failed disk - dev_roles[X]
read errors - may change: dev_roles[X], recovery_offset
array checks - normally won't change, except disk fail is detected
commands by user - depend on special cmd
If an array operates fine for months - without user intervention - won't change

at last, please read the code.

Thanks.