If a system with mirrors for root (/), /usr, and swap, the so-called “boot” file systems, is booted into single-user mode (by using the boot -s command), these mirrors and possibly all mirrors on the system will appear in the “Needing Maintenance” state when viewed with the metastat command. Furthermore, if writes occur to these slices, the metastat command shows an increase in dirty regions on the mirrors.
Though this situation appears to be potentially dangerous, there is no need for concern. The metasync -r command, which normally occurs during boot to resynchronize mirrors, is interrupted when the system is booted into single-user mode. Once the system is rebooted, the metasync -r command will run and resynchronize all mirrors.
If this is a concern, run the metasync -r command manually.