What is scsid?

scsid is a storage-related process you might see in Activity Monitor.

What is scsid?

scsid handles SCSI (Small Computer System Interface) communication on your Mac. SCSI may sound old, but its command set is still the basis for how macOS talks to storage devices, including modern USB drives, Thunderbolt storage, and even some internal drives.

Is SCSI still used?

The original SCSI cables and plugs are long gone, but the SCSI command language lives on. When your Mac reads from or writes to a USB flash drive, the commands are sent as SCSI over USB (the USB Mass Storage protocol wraps SCSI commands). Thunderbolt storage and many other connections use SCSI commands too.

When does it run?

scsid is involved when your Mac talks to storage devices, mainly external drives connected by USB or Thunderbolt. The internal SSD uses NVMe, which has its own command set.

Does it use many resources?

No. It handles command translation and device communication at a low level, with very little CPU use.

Should you worry?

No. It is a standard macOS storage process. The SCSI command set is a long-standing standard that underpins most external storage connections.

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