Linux RAID mdadm: what does ‘Events’ mean

linuxmdadmraidraid1

When I type

mdadm –detail /dev/md0

I get a lots of useful information most of which I understand. However I also get a line that reads:

Events : 0.710

Where the number varies.

Naively, I thought an event either happened or it didn't. How can I have only 0.710 of an event? Or if you prefer why is "Events" not an integer value?

EDIT

After seeing user's answer below, I dug into the code a bit and found

`#if __BYTE_ORDER == __BIG_ENDIAN

144 __u32 events_hi; /* 7 high-order of superblock update count */

145 __u32 events_lo; /* 8 low-order of superblock update count */

…

148 #else

149 __u32 events_lo; /* 7 low-order of superblock update count */

150 __u32 events_hi; /* 8 high-order of superblock update count */

…

153 #endif`

So "Events" is high-order and low order of "superblock update count" https://raid.wiki.kernel.org/index.php/Superblock

Best Answer

It's actually 2 integers.

printf("\n         Events : %d.%d\n\n", sb->events_hi, sb->events_lo);

events_hi and events_lo are counters of the update events their sum is the total md events, the hi and lo (I ASSUME, without looking further into the code) represent the "significance" of the update.

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