On Fri, Mar 07, 2014 at 11:39:40AM +0000, bugzilla-daemon@xxxxxxxxxxxxxxxxxxx wrote: > JFS provides three modes, journal, ordered and writeback. > The first mode is denoted as ‘journal mode’in the following context. > In the journal mode, data should be written twice, one for the journal area and > the other for the client file system. If the journal area and the client file > system are both located in the disk, it has at least 50% performance > degradation compared to ordered mode. > But what if we put the journal area in a ramdisk? How big was the ramdisk? Since all of the blocks are going through the journal, even if it is on the journal, it requires more commits and thus more checkpoint operations, which means more updates to the disk. A bigger journal will help minimize this issue. Would you be willing to grab block traces for both the disk and the external journal device? I will add that the workload of "dd if=/dev/zero of=file" is probably the worst case for data=journal, and if that's really what you are doing, it's a case of "doctor, doctor, it hurts when I do that". All file systems modes will have strengths and weaknesses, and your use case one where I would simply tell people, "don't use that mode". If you want to work on improving it, that's great. Gather data, and if we can figure out an easy way to improve things, great. But I'll warn you ahead of time this is not necessarily something I view as "unreasonable", nor is it something that I would consider a high priority thing to fix. - Ted -- 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
