Dalibor Straka wrote:
On Sat, Apr 02, 2005 at 10:11:21PM -0800, Tony Godshall wrote:Note. You should never use XFS (or JFS or others of that class of journaling file system, which I believe are meta data journaling) unless the machine is connected to an UPS. ...Huh? One of the main strengths of journaling filesystems is that they do recover from poor shutdown better... theExactly!
I forget where I read it (I believe it was an old LKML posting), but some guy from SGI was trying to explain to people that were experiencing corruption with XFS that it should only be used on systems with an UPS. The problem is not the file system, but the hardware. He said when the average system loses power, the RAM almost immediately turns to crap (in terms of content), but the hard drive (much less voltage sensitive) will continue to write long after the RAM has stopped delivering valid bits (his words). The issue is that ext3 journals the data (i.e., the actual bits you intend to write to disk). However, XFS (and JFS and ReiserFS) journal the metadata (the location, size and checksum of your write operation), not the data itself. If the hard drive writes crap to the platter, metadata journalling does you no good. The guy from SGI that posted to LKML said that SGI worked around the problem in hardware by enlarging the capacitors between the power supply and the RAM and other components as necessary so that in the event of a power failure all components go dead at the same time. So yes, journaling helps you with a crash, but ext3 is best suited to handle the poor quality of consumer-grade hardware. -Roberto -- Roberto C. Sanchez http://familiasanchez.net/~sanchezr
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