| Pat Regan on 30 Dec 2005 20:49:55 -0000 |
|
Tom Diehl wrote: >> The adapter boards are inexpensive and there are HW raid versions that >> are in the $100 range. > > Most of these are NOT true hardware raid. They are software raid in hardware > raid's clothing. Adaptec, promise, etc. are famous for this. > > 3Ware is one manf. of true hardware raid controllers (for more $$ of course). > With true hardware raid the OS only sees a single drive. The disks are managed > by the controller. > I have yet to use an SATA 3ware card, but all the 3ware cards I have used in the past were wonderful. > I am not saying the fake raid controllers are necessarily bad, just that you > should be aware of the difference. > The fake raid controllers scare me a little bit. I assume this isn't true of all fake raid cards... But it is my understanding that many (most?) fake raid cards work just fine with both raid and non-raid drivers. Meaning that if you somehow manage to boot your OS with the wrong driver you might blow up your array (if you also manage to write something to one of the disks). I suppose something similar can happen with software raid, but I imagine most people expect their raid controller to prevent getting into this situation :). >> When using HW raid... lets say 2 drives mirrored for a simple example. >> Assuming there are 6 or 7 linux partitions on the drive, does it treat the >> drive as one entity? E.G if you were to lose a drive and replace it would >> it reconstruct it as the other drive with all partitions? > > Yes, even software raid will do this if configured properly. One of the nice things about software raid is flexibility. I am currently on a very tight budget at home. I wanted to improve my disk throughput without sacrificing much space. I have a 3ware 7800 controller and 3 160 gig IDE disks in my desktop. Due to the times they were added to the machine, I was running a RAID 1 on 2 disks, and the third disk was just a JBOD on the 3ware card. I tore that all down, left all 3 drives on the 3ware card and switched to software RAID (plus LVM). My primary OS and home paritions are a RAID 0 of the first 10 gig or so of each drive. The rest is RAID 5. I have an rsync style backup mirroring the RAID 0 a few times a day to a bootable RAID 5 partition. Everything I can't live without is stored on the RAID 5 :). My unscientific read throughput test using dd gives me about 125 MB/sec on the RAID 0 (individual drives push about 55 MB/sec). I was curious if I was hitting a bottleneck on the 3ware card (it is a 64 bit card in a 64 bit slot). So I moved one of the drives to my on board IDE. My unscientific dd test slowed to about 80 MB/sec, which surprised me :). Sorry for drifting a bit off the topic there, I just figured it might be interesting to someone :p. Pat Attachment:
signature.asc ___________________________________________________________________________ Philadelphia Linux Users Group -- http://www.phillylinux.org Announcements - http://lists.phillylinux.org/mailman/listinfo/plug-announce General Discussion -- http://lists.phillylinux.org/mailman/listinfo/plug
|
|