Mark Knecht wrote: >On my 3 1394 drives I get about 18MB/S, 24MB/S and 24MB/S. The 18MB/S >drive is the oldest (and smallest at 40GB) of the three. > >
Cool, thanks for the info. I just realized that the only sensible configuration is to move my 3.5" backup drives to the 1394, because my laptop only has the unpowered 4-pin mini-connector. Since I have to have AC power for the backup drives anyway, they are the logical choice for that bus. >OK, so I'll bite. If you don't actually read all three disks then how >do you know they all contain the same data? I'm concerned that there >could be a time when data is written and it's corrupted due to >problems in the 1394 sub system. I assume for now that these >corruptions are random and do not happen on all three cables. How do I >guard against that? > > The md (aka RAID) driver uses it's own on-disk 'format' to store configuration information (like the UUID of the raid array, what element this device is in the array, a timestamp of when it was last seen, etc) and also to track which drive has the freshest data. If the array is not in degraded mode, it optimizes reading for speed, since each disk is supposed to contain the same data. If it is in degraded mode, then it needs to check which disk has the freshest data, and returns that. Of course, it should also by resyncing the array, so that each drive gets updated with the right data. Obviously, an array resync can take a very long time, so you really want to use a journalled filesystem because you do *not* want to wait for an fsck and an array resync to run simultaneously. >I know the drives themselves are good as I've used them all under >Windows for quite a long time with no lost data ever. (Yea FAT32!) ;-) >However I have lost data once already under Linux using ext3. The >system said it was moving a 1GB file, however it finsihed with no >error messages in 1 second and while there was a file icon on the >target drive the system said the file was corrupted and couldn't read >it. > > Well, from what I know, the md driver pretty much assumes that either the data it sent over the cable made it to the disk, or that the disk/controller noticed something wrong and signalled an error. I doubt RAID1 will help you with silently disappearing data. -Richard -- gentoo-user@gentoo.org mailing list
