Hi, I recently setup raid10 on 4 physical disk and have a iscsi serve it as a block device, and have been trying to tweak for performance. First thing I notice that MD seems to rely on page cache to flush changes to disk, is there any way to turn that off so changes are flushed to the disk? like O_FSYNC|O_DIRECT does? The reason I want to turn it off is to understand the performance difference, I want to be sure that page cache is truly acting as a write-back cache, I know one can tune the dirty_* to control the cache flush, but I want to make sure that it is actually doing what I think it does. Then I notice in output of free, the number in Cache column is very low, however the Buffer is very high, my question is does Buffer here serves as a read cache? I couldn't find the answer anywhere else. My last question is that since MD seems already doing the cache, what effect would it have if I want to setup a LO device in front of MD device, Is there going to be more caching, how is different than just plain MD device? Thanks. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
