Its good to knows ones limitations.
Yes, it is OK to use Time Machine with a drive that is only occasionally available. Backup will resume when you turn the drive on. You can either wait for the backup to start, or you can click "backup now" on the TM icon. You might consider a networked attached drive in the future that is located away from your work area. That would allow the drive to stay on without you hearing it, and backup to run unattended.
/Jim
I'm looking into that as we speak. Hopefully I'll have something better set up by next month.
Is the external an all in one unit? If so there isn't much you can do. If it won't spin down it won't.
If it's in a caddy you can remove it from, better caddies have a chip that allow the drive to sleep. I guess you either sell your all in one a buy a new drive and a caddy, or put up with the noise.
Somehow I doubt I'll find a better caddy. It's an ancient hard drive that I got for free from an old workplace. Specs from System Information:
OXFORD IDE Device:
Manufacturer: Oxford Semiconductor Ltd.
Model: 0x1
GUID: 0x30E006E044315D
Maximum Speed: Up to 400 Mb/sec
Connection Speed: Up to 400 Mb/sec
Sub-units:
OXFORD IDE Device Unit:
Unit Software Version: 0x10483
Unit Spec ID: 0x609E
Firmware Revision: 0x102
Product Revision Level: WK10
Sub-units:
OXFORD IDE Device SBP-LUN:
Capacity: 300.07 GB (300,069,052,416 bytes)
Removable Media: Yes
BSD Name: disk4
Partition Map Type: APM (Apple Partition Map)
S.M.A.R.T. status: Not Supported
Volumes:
disk4s1:
Capacity: 32 KB (32,256 bytes)
BSD Name: disk4s1
Content: Apple_partition_map
Hardbox 300GB:
Capacity: 299.93 GB (299,934,793,728 bytes)
Available: 293.45 GB (293,453,574,144 bytes)
Writable: Yes
File System: Journaled HFS+
BSD Name: disk4s3
Mount Point: /Volumes/Hardbox 300GB
Content: Apple_HFS