The backup is applied to a standard, non-encrypted APFS container on an external USB 3.x drive. This drive has one other APFS container that I use for backup up general data. There is no other real activity there.
Something associated with the mds processes is accessing the drive on a fairly regular basis. I do have regular TM backups that occur via normal automation provided by the Apple Time Machine subsystem.
Whatever activity is taking place is causing some other apps to spike in CPU consumption. This seems random, but is fairly consistent.
I ran pmset -g assertions:
2022-03-29 13:27:14 -0400
Assertion status system-wide:
BackgroundTask 1
ApplePushServiceTask 0
UserIsActive 1
PreventUserIdleDisplaySleep 0
PreventSystemSleep 0
ExternalMedia 1
PreventUserIdleSystemSleep 0
NetworkClientActive 0
Listed by owning process:
pid 183(WindowServer): [0x0000001b00098185] 00:00:00 UserIsActive named: "com.apple.iohideventsystem.queue.tickle serviceID:100000784 name:AppleHIDKeyboardEve product:Apple Internal Keyb eventType:3"
pid 121(powerd): [0x00000018000880ac] 119:15:08 ExternalMedia named: "com.apple.powermanagement.externalmediamounted"
pid 1907(mdsync): [0x00000069000b847a] 119:13:47 BackgroundTask named: "com.apple.metadata.mds.scan"
Kernel Assertions: 0x104=USB,MAGICWAKE
id=506 level=255 0x4=USB creat=3/24/22, 2:22 PM description=com.apple.usb.externaldevice.01200000 owner=Mercury Elite
id=507 level=255 0x100=MAGICWAKE creat=3/24/22, 2:15 PM description=en0 owner=IOSkywalkNetworkBSDClient
id=508 level=255 0x100=MAGICWAKE creat=3/24/22, 2:23 PM mod=3/29/22, 1:21 PM description=llw0 owner=IOSkywalkNetworkBSDClient
Idle sleep preventers: IODisplayWrangler
Mercury Elite is the external drive, which I obtained from OWC. It is 18B in size.
I have had this same configuration during Big Sur and I did not have these problems. They only started manifesting after recent updates to MacOS Monterey. Therefore, through process of elimination, I am assuming something changed.
In searching Google, there are several other similar reports that have to do with MDS, but I can't see a common pattern that connects to usage of the system.
I believe my next option is to re-install the system to Big Sur and wait for Monterey to become stable, unless a fix is forthcoming.