Are disk sector writes atomic?

Question

Clarified Question:

When the OS sends the command to write a sector to disk is it atomic? i.e. Write of new data succeeds fully or old data is left intact should the

Answer 1

Nobody seems to agree on this question. So I spent a lot of time trying different Google queries until I finally found an answer.

from Dr. Stephen Tweedie, RedHat employee and linux kernel filesystem and virtual memory developer in a talk on ext3 (which he developed) transcript here. If anyone knows, it'd be him.

"It's not sufficient just to write the thing to the journal, because there's got to be some mark in the journal which says: well, (has this journal record actually) does this journal record actually represent a complete consistency to the disk? And the way you do that is by having some atomic operation which marks that transaction as being complete on disk" [23m, 14s]

"Now, disks these days actually make these guarantees. If you start a write operation to a disk, then even if the power fails in the middle of that sector write, the disk has enough power available, and it can actually steal power from the rotational energy of the spindle; it has enough power to complete the write of the sector that's being written right now. In all cases, the disks make that guarantee." [23m, 41s]