A readable volume can provide names, sizes, and supported file information even when it does not permit changes.
Read-only states include optical media, locked disk images, write-protected storage, some network shares, and volumes mounted read-only after errors.
Use analysis to understand contents, but expect deletion, metadata changes, and organization actions to fail.
If the disk should be writable, back up important data and use appropriate Finder, Disk Utility, server, or administrator diagnostics.
Do not force-write a volume mounted read-only because of corruption. Repair or replace it through supported storage procedures.