Toby Thain wrote:
On 19-Jul-06, at 11:27 AM, Payal Rathod wrote:
Hi, ...
And lastly don't the journalling fs give a false sense of security to
the user, saying that the data is written to disk when in reality only an
entry is made in journal and data is still not committed to disk.
This last one is easy to answer: No. Regardless of the filesystem you're
using, there is no guarantee your data hits the disk until you fsync().
Journalling filesystems don't change this. (And even after that, it
depends on the device doing the right thing :)
Interestingly, most modern IDE hard drives can not turn off write
caching. But, I'm guessing they have a big enough capacitor to flush
that if you lose power.
I often turn off fsync, because it gets too abused. There was a bug in
Evolution where, when dragging columns, every time the display refreshed
(as you were dragging), it would flush and fsync. Now tell me, do I
really need to be absolutely sure that, when recovering from a crash, my
Evolution column widths are EXACTLY where they were while I was dragging
the columns?
My philosophy is, unless you have a UPS device, loss of power will
always result in lost data. Crashes will also more often than not
result in lost data. So do frequent backups and have a
managed/monitored UPS, so that when you lose power, your system flushes
everything to disk and shuts down.
