Blake Barnett([EMAIL PROTECTED])@2002.01.18 13:59:24 +0000: > On Fri, 2002-01-18 at 12:13, [EMAIL PROTECTED] wrote: > > Are you certain it's faster? I don't know much about the particulars of how > > ext3 is implemented, but I was under the impression that a slight performance > > hit was the tradeoff for journalling.
It depends on the definition of journalling :) ext3 has 3 different modes, only in one mode it does full data journaling, so in that mode your data is safe. In ordered mode, your file meta-data is journaled, your data may not reach the disk, but you won't have old data in your files (or even data from different files). And writeback mode means, that your filesystem structure is guaranteed tom be consitent at any time, so your fsck does not have to check the disk, just replay the journal up to the first bad transaction. This means your fsck-time will be very short which is good for todays large drives. see below for explanation (from mount(8)) > >From listening to Andrew Morton talk about it, he said that much more > work has been put into ext3 for optimization than for ext2, so for some Small to medium writes can actually be faster anyway: you just write append data to the journal, you have no head movement on your disk. Once it's written to the journal write() returns and to your application it seems fast. A few seconds later the journal is written out to the actual position on disk. Hope this helps ... Benno ----- snip ----- "mount -o data=journal" Journals all data and metadata, so data is written twice. This is the mode which all prior versions of ext3 used. "mount -o data=ordered" Only journals metadata changes, but data updates are flushed to disk before any transactions commit. Data writes are not atomic but this mode still guarantees that after a crash, files will never contain stale data blocks from old files. "mount -o data=writeback" Only journals metadata changes, and data updates are entirely left to the normal "sync" process. After a crash, files will may contain stale data blocks from old files: this mode is exactly equivalent to running ext2 with a very fast fsck on reboot. -- Sebastian Benoit <[EMAIL PROTECTED]>
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