Home Forums Peripherals & Multimedia Peripherals Time Machine: HDD vs. SSD

If my understanding is correct, HDDs can be overwritten many times in each sector but SSDs, when nominally overwritten, actually have the data written to a different section. Since Time Machine can fill up space and then the oldest backup is deleted and overwritten, does this make TM more suited to a HDD than a SSD?

Time Machine is probably more suited to an HDD because:

• HDDs retain the data langer before it begins to deteriorate
• HDDs curently are available in higher capacities than SSDs
• HDDs are a lot cheaper than SSDs any way you measure cost
• Read/write speed is typically not an issue with Time Machine backups

Thanks, Joe. Your points are along the lines that I was thinking.

Another thought for your consideration. Although SSD prices have come down significantly HDDs are getting really cheap in high capacities. For Time Machine backups where reliability is THE key feature you can get a RAID enclosure populated with HDDs for about the same money or less than a single SSD and enclosure, and assuming RAID 1 or RAID 5 if a drive fails (which they will) your Time Machine backup is still good. I use just such an array running SoftRAID and configured RAID 5 that I use for Time Machine backups. When one of the drives in the array failed a hot swap with a new drive of the same capacity and SoftRAID automatically rebuilt the failed drive without missing a beat or a backup cycle. You can't beat that for backup reliability.

A final tidbit when considering Time Machine drives: APFS is optimized for use with SSDs, but APFS does not support hard links and Time Machine backups use a massive amount of hard links, so you cannot use a drive formatted APFS for Time Machine backups. I don't know Apple's roadmap for Time Machine development but given some of the features of APFS there might well be an APFS hosted Time Machine 2 in a future version of MacOS which might tilt the scales in favor of SSD drives for Time Machine. In the meantime the only change I might make in my RAID array is to replace the four 1TB drives with higher capacity HDDs.