On Sat, Nov 10, 2012 at 10:58 AM, Theodore Ts'o <tytso@xxxxxxx> wrote: > On Sat, Nov 10, 2012 at 12:40:42AM +0000, Nelson, John R wrote: >> Hi, >> Say if ext4 commits every 5 seconds, does this mean whatever is >>buffered for delayed allocation is flushed every 5 seconds as well? > > No; there is a separate 30 second timer which is used for writeback > thread. > > For ext3 in data=ordered mode, we will flush out dirty pages for > inodes which have been written to make sure that stale data can never > get revealed. > > But in delayed allocation, there is no risk that stale data can get > revealed until we actually allocate the data blocks. > Hi Ted, Then ext4.txt seems need updating? If I understand you correctly, I'd expect to lose 30 seconds of data rather than 5 seconds if data is delayed allocated. 172 commit=nrsec (*) Ext4 can be told to sync all its data and metadata 173 every 'nrsec' seconds. The default value is 5 seconds. 174 This means that if you lose your power, you will lose 175 as much as the latest 5 seconds of work (your 176 filesystem will not be damaged though, thanks to the 177 journaling). This default value (or any low value) 178 will hurt performance, but it's good for data-safety. 179 Setting it to 0 will have the same effect as leaving 180 it at the default (5 seconds). 181 Setting it to very large values will improve 182 performance. -- Thanks, Tao -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
