Yo Rich! On Fri, 21 Jun 2013 13:57:20 -0400 Rich Freeman wrote: > In theory it could be done that way, but every > raid1 implementation I've heard of makes writes to all drives > (obviously), but reads from only a single drive (assuming it is > correct). That means that read latency is greatly reduced since they > can be split across two drives which effectively means two heads per > "platter." Yes, that is what I see in practice. A much reduced average read time. And if you are really pressed for speed, add more stripes and get even more speed. > Also, raid1 typically does not include checksumming, so if > there is a discrepancy between the drives there is no way to know > which one is right. Uh, not exactly correct. Remember each HDD has ECC for each sector. If there is a read error the HDD will detecct the bad ECC and report the error to the RAID1 hardware/software. Then RAID1 is smart enough to try to read from the 2nd drive. > With raid5 at least you can always correct > discrepancies if you have all the disks Not really. If 2 disks fail in an n+1 RAID5 you are out of luck. Not as uncommon occurance as one might think. > (though as Duncan pointed out > in practice this only happens if you do an explicit scrub on mdadm). Which you should be doing at least weekly. Otherwise you only find out your disks have failed when you try to do a full copy or backup, and then you likely have multiple failures and you are out of luck. RGDS GARY --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701 gem@rellim.com Tel:+1(541)382-8588