From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Masover Subject: Re: somewhat OT query on journalling Date: Wed, 19 Jul 2006 14:09:15 -0500 Message-ID: <44BE835B.7020806@slaphack.com> References: <20060719152744.GA26155@tranquility.scriptkitchen.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: list-help: list-unsubscribe: list-post: Errors-To: flx@namesys.com In-Reply-To: List-Id: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Toby Thain Cc: reiserfs-list@namesys.com 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.