Disabling Hard Disk caches on individual drives?

Dan Egli ddavidegli at gmail.com
Wed Apr 3 02:46:24 MDT 2013

*on Monday, April 1, 2013, at 4:09 PM, Nicholas Leippe wrote:*

* *

*> These below should, if supported by the device:*

* *

*Thanks! That's just what I was looking for!*

* *

*--- Dan*

On Mon, Apr 1, 2013 at 4:09 PM, Nicholas Leippe <nick at leippe.com> wrote:

> On Mon, Apr 1, 2013 at 2:20 AM, Dan Egli <ddavidegli at gmail.com> wrote:
> >
> > *Something that was mentioned a week or two back and I meant to follow up
> > but never did was changing cache mode for Linux's disk writes. How does
> one
> > accomplish that and can it be done on an individual drive basis? I.e.
> > Suppose I am using a set of hard disks in USB3 or eSATA enclosures to
> > backup my home system. If I backup the entire raid (i.e. dd if=/dev/md0
> > of=/dev/md1) then how do I make sure that all the data was properly
> written
> > to the drives in md1 before I disconnect the drives and turn them off
> > (since they're in enclosures I can simply turn the enclosures off)? I
> don't
> > want to write that way, only to assume that everything is OK and find out
> > later that something didn't get written right. And yes, I know I could
> > simply do an individual file backup, and that's on the agenda too. But
> even
> > then, unless unmounting the md1 would force all cached data to be written
> > immediately anyway. But I am considering both options.  So I would
> > appreciate it if someone could explain to me (since I've never tried
> > before) how you can go about disabling write caching to an individual
> drive.
> umount # forces all data to be written
> sync # also forces all data to be written
> The above two may not cause underlying block device to commit caches.
> These below should, if supported by the device:
> hdparm -F
> sdparm -C sync
> sdparm --clear=WCE
> other options may also exist
> Also, some external enclosures interfere with reading/setting some or
> all options that the underlying drive may actually provide. YMMV.
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