> Goswin von Brederlow writes: : > Dean Mesing writes: : > If I'm using an ext3 filesystem (which I plan to do) would Full and : > Incremental dumps to a cheap 'n big USB drive (using the dump/restore : > suite) not work? : : Probably. But why not rsync? It will copy all changes and the data on : the USB disk will be accessible directly without restore. Very handy : if you only need one file. I don't see how one would do incrementals. My backup system uses currently does a monthly full backup, a weekly level 3 (which saves everything that has changed since the last level 3 a week ago) and daily level 5's (which save everything that changed today). I keep 3 months worth of these. So basically if a file existed for more than 24 hours w/in the last three months I've got it somewhere in my backup partition. If I accidently delete a file and don't notice it for 10 days, no problem. I'm not sure rsync can do this. (I already use rsync to keep various directories on my 5 machines in sync). : If it works right, and the numbers are probably obviously wrong if : not, you can see the number of bad blocks. If that starts rising then : you know the disk won't last long anymore. But when was the last time : one of your disks died by bad blocks apearing? Mine always sieze up : and won't spin up anymore or the heads won't seek anymore or the : electronic dies. Never had a disk where the magnetization failed and : more and more bad blocks appeared. Actually I've never had a disk stop spinning. It's always other stuff where it stops doing I/O or gives corrupt data. : Untuned I have this: : : # cat /proc/mdstat : Personalities : [linear] [raid0] [raid1] [raid10] [raid6] [raid5] [raid4] : md1 : active raid5 sdd2[3] sdc2[2] sdb2[1] sda2[0] : 583062912 blocks level 5, 64k chunk, algorithm 2 [4/4] [UUUU] : # blockdev --getra /dev/sda : 256 : # blockdev --getra /dev/md1 : 768 : # blockdev --getra /dev/r/home : 256 : : You see that the disk and LV is at the default of 256 blocks read : ahead. But the raid it at (4-1)*256 == 768 blocks. : : You usualy can still raise those number a good bit. Esspecialy if you : are working with large files and streaming access, like movies. :) Someone on the Fedora list who is running 4 50 MB/s drives in RAID 5 array was getting read speeds of 120 MB/s or so. Not 300% but not to bad. He also had an untuned md device readahead of 768. With 3 devices I have an un-tuned one of 512, but going to 768 makes little difference. I must go up to 16384 to see any decent read improvement. I wonder why four drives works so much better than three. <snip> : I hope you are sufficiently scared now to consider all the : consequences. You seem to plan doing regular backups. That is : good. That means what you actualy risk with raid0 (or imho preferably : striped lv) is loosing yesterdays work and todays time to restore the : backup. Now you can gamble that you won't have a disk failure too : often, maybe not for years and the speedup of plain raid0 will save : you more time commulative than you loose in those 2 days. I'm not sure if I could quantify the time savings quite so pragmatically. But using a very snappy machine is simply a pleasure. That counts for something. I'm not afraid of restoring if I need to. : I probably will. But due to Murphys law the failure will happen at the : worst time and obviously you will be mad as hell at that time. For a : single person and a single raid it all comes down to luck in the end. Agreed. The other option, if I can swing it with my boss, is to purchase a 3ware true hardware RAID-5 card that presents the disks as one device. They are about $450 and the RAID-5 runs (from what I hear) quite fast for both read and writes (uses write-back with battery backup to get write speeds up). But you've given me some things to explore regarding RAID-10 and LV striping. Thanks. : At work we just got a job of building a storage cluster with ~1000 : disks. At that size the luck becomes statistics. A "the disk will : probably not fail for years" becomes "10 disks will die". So my : outlook at raid saftey might be a bit bleak. With that many disks, one is sure to fail every month or so unless they are top quality drives. Thanks again. Dean - 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
