Disk write atomicity (was: NTFS fault tolerant?)

NTFSD
1

Except when you pull the plug out of the wall in the middle of the write,
or the drive experiences a failure of hardware or firmware, including
transient error conditions like thermal asperities, yes, a single sector
is committed to the platters atomically.

:slight_smile:

Phil

Philip D. Barila
Seagate Technology LLC
(720) 684-1842

xxxxx@lists.osr.com wrote on 01/24/2005 03:50:16 PM:

This may be a bit off topic here, but on a related note, do any of you
guys
know whether most disk devices today gaurantee atomicity of sector
writes
(i.e., a sector of data can never be half written; it’s either all
written
or all not written) ?

Matt

2

Phil,
Just to confirm, what you are saying is that hard disk device
manufacturers (including Seagate) DO NOT engineer any features into the
drives that would insure atomic sector writes in the event of any type of
failure mode such as loss of power. In other words, they don’t go to any
extra lengths to insure atomicity for certain failure cases.

Thanks,
Matt

From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com] On Behalf Of
xxxxx@seagate.com
Sent: Tuesday, January 25, 2005 5:05 PM
To: Windows File Systems Devs Interest List
Subject: [ntfsd] Disk write atomicity (was: NTFS fault tolerant?)

Except when you pull the plug out of the wall in the middle of the write, or
the drive experiences a failure of hardware or firmware, including transient
error conditions like thermal asperities, yes, a single sector is committed
to the platters atomically.

:slight_smile:

Phil

Philip D. Barila
Seagate Technology LLC
(720) 684-1842

xxxxx@lists.osr.com wrote on 01/24/2005 03:50:16 PM:

This may be a bit off topic here, but on a related note, do any of you
guys
know whether most disk devices today gaurantee atomicity of sector writes
(i.e., a sector of data can never be half written; it’s either all written
or all not written) ?

Matt
— Questions? First check the IFS FAQ at
https://www.osronline.com/article.cfm?id=17 You are currently subscribed to
ntfsd as: xxxxx@bitarmor.com To unsubscribe send a blank email to
xxxxx@lists.osr.com

3

That’s what battery backed caches are for. The drive will use what little
rotational energy remains in the spindle to park the heads, there is not
sufficient energy to reliably complete a sector write. The state of the
sector being written at the time of power interruption is indeterminate.

Phil

Philip D. Barila
Seagate Technology LLC
(720) 684-1842

xxxxx@lists.osr.com wrote on 01/25/2005 03:59:22 PM:

Phil,
Just to confirm, what you are saying is that hard disk device
manufacturers (including Seagate) DO NOT engineer any features into
the drives that would insure atomic sector writes in the event of
any type of failure mode such as loss of power. In other words,
they don’t go to any extra lengths to insure atomicity for certain
failure cases.