Post, Mark K writes: > Since ext3 is advertised as "ext2 with a journal," I would say that the > journal is the only additional overhead you'll see in terms of disk space > usage.
Hmm, "sort of". From the point of view of purely disk space usage, that's true, as you say. Further, ext3 is indeed "ext2 with a journal", so you're right there too. The reason for the "sort of" is that what "ext2" means there is a little more ambiguous than you might imagine. During ext2's development history, a number of changes have been made to improve performance. Some of those have been folded into ext3 and some haven't. If you want to make an accurate comparison of ext2 and ext3, you may find in practice that those differences become significant for some workloads. Three of the changes which spring to mind are * htree indexing (from Daniel Phillips) for faster directory lookups * the Orlov allocator for choosing where to allocate disk blocks for new files (i.e. when do you put them "near" recently created files to get good locality of reference and when do you put them far away in order to allow room for the files to expand without fragmentation) * locking (if I recall, the locking requirements for the journalling sometimes means the kernel has to (or wants to) do the locking in the ext3 filesystem differently from ext2. What I can't remember is which changes were carried across from ext2 to ext3 and when. There's also the difference that the journal I/Os will affect the I/O scheduling for the ordinary filesystem I/Os themselves unless the journal has been placed somewhere else carefully enough. All in all, I'd suggest people do some thinking, testing and measuring when moving from ext2 to ext3 if the workload is I/O intensive enough that it might make a difference. --Malcolm -- Malcolm Beattie <[EMAIL PROTECTED]> Linux Technical Consultant IBM EMEA Enterprise Server Group... ...from home, speaking only for myself ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390
