On Sun, 9 Jan 2005, Guy wrote: > Why is RAID1 preferred over RAID5? > RAID1 is considered faster than RAID5. Most systems tend to read much more > than they write. You'd think that, wouldn't you? However, - I've recently been doing work to graph disk IO by reading /proc/partitions and feeding it into MRTG - what I saw surprised me, although it really shouldn't. Most of the systems I've been graphing over the past few weeks write all the time and rarely read -I'm putting this down to things like log files being written more or less all the time, and the active data set residing in the filesystem/buffer cache more or less all the time. (also ext3 which wants to write all the time too) However, I guess it all depends on what the server is doing - for a workstion it may well be the case that it does more reads. Have a quick look at http://lion.drogon.net/mrtg/diskIO.html This is a moderately busy web server with a couple of dozen virtual web sites and runs a MUD and several majordomo lists. Blue is writes, Green reads. Note periods of heavy read activity just after midnight when it does a backup (over the 'net to another server and it also sucks another server onto the 'archive' partition), and 2am is when it analyses the web log-files. Also note that it's swapping - this has 256MB of RAM and is due for an upgrade, but swap is keeping it all ticking away nicely. The var partition seems to sustain writes at approx. 200-300 sectors/second... Not a fantastic amount, but I found it rather surprising. (I'll put the MRTG code online for anyone who wants it in a few days and let you know) Gordon - 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
