Drop the RAID 5 and go with a RAID 10 as you were talking about but add a hot spare if you can. RAID 10 doesn't have a parity bit which slows down write times. But if a disk is bad and isn't replaced you can have a bad day. Hot spares have saved my butt more than once.
Regards, Dain Bentley -----Original Message----- From: keith [ke...@scott-land.net] Received: Monday, 16 Jan 2012, 12:14pm To: Joel Sing [j...@sing.id.au] CC: misc@openbsd.org [misc@openbsd.org] Subject: Re: Softraid & raid 5 throughput problem On 16/01/2012 15:43, Joel Sing wrote: > On Monday 16 January 2012, keith wrote: >> I built a storage server to run the Bacula storage daemon on. My plan >> was to boot of a usb key then to use the four 2TB sata disks that are in >> the server as a softraid raid 5 volume. The server in question is a dell >> poweredge R310, i3 CPU 540 @ 3.07GHz with OBSD 5.0 amd64. >> >> I put the OS onto the usb key but the softraid 5 volume seemed realy >> slow. Sftping files over the local network to the servers softraid >> volume was taking ages. So as I was short of time I just rebuilt the >> server installing OBSD into one of the sata disks wd0 >> >> Later I connect to the server and made a raid5 volume on the remaining >> three disks but the speed was really slow to I tried a raid1 on two of >> the disks and that works fine speed wise. >> >> I've tried to get some stats to figure out what's going on >> >> raid 5 (wd1, wd2,wd3) Time for newfs command to complete = 1 min 14 secs >> raid 5 (wd1, wd2,wd3) Time to copy 2.3G file from wd0 onto the softraid5 >> disk = 5 mins ish >> >> raid 1 (wd1, wd2) = 1.8TB Time for newfs command to complete = 4 secs >> raid 1 (wd1, wd2) copy 2.3G Time to copy 2.3G file from wd0 onto >> softraid disk = 25 secs > RAID 5 with softraid(4) is not ready for primetime - in particular it does not > support scrub or rebuild. If you have a single disk failure you will get to > keep your data, however you will need to dump/rebuild/restore. > > I'm not specifically aware of performance issues, but I'm not entirely > surprised either - I'll try to take a look at some point. RAID 5 writes will > be slower, but not that much slower... > >> As this point I though I'd try raid0 but the server went and hung for >> some reason. >> >> #bioctl -d sd0 >> #bioctl -c 0 -l /dev/wd2a,/dev/wd3a softraid0< It hung on this >> command.... Won't know what happed till I get to the datacenter. > I'm guessing that you did not clear the existing RAID 1 metadata first, in > which case you'll probably have a divide by zero with a trace that ends in > sr_raid1_assemble() - there is a bug there that I hit the other night. > >> Idealy I wanted one large disk but if can't get a quick raid5 working I >> will just use two softraid raid 1 disks and work around it. Does anyone >> have any suggestions ? > I'd stick with RAID 1 - you can use more than two disks, which will give you > increased redundancy and should improve read throughput. Obviously you'll > have less capacity though. Thanks for the quick answers, If I just create two raid 1 sets on the server then could I just make a raid 0 volume using both raid1's ? Thanks Keith
