Sorry, I just replied to one msg not to the group.. anyway: for you Matt: Mostly they recommend raid 1+0 or raid 1 + hotspares.. or raid5 with more then 4 discs (has that to do with smaller datablocks/stripe or the higher troughput??).. otherwise performance can be very bad..
At least that was in the recommendations of my postgres serverpart.. cheers.. Op dinsdag 09-03-2010 om 23:23 uur [tijdzone +0000], schreef Jefferson Ogata: > On 2010-03-09 23:12, Matt Domsch wrote: > > On Tue, Mar 09, 2010 at 04:54:44PM -0600, John G. Heim wrote: > >> Has anyone configured a database server with RAID-5? Is it really a bad > >> idea > >> to do so? I asked last month for tips on configuring a DB server. I have > >> around $6K to spend. I am pretty much settled on getting 2 quad-core CPUs > >> and 32 Gb of RAM. But I'm still ignorant in terms of what to get for disk. > >> 1500 RPM, I know that. But is it better to do RAID-1 or RAID-5. I can't > >> figure out why RAID-1 would be better than RAID-5. I understand that with > >> RAID-5, a single database write might translate into writing 2 blocks (a > >> data block and a parity block). But doesn't RAID-1 *always* do an extra > >> write for every data block written? > > > > RAID 5's problem isn't the extra write. It's that to write a hunk > > that's not a whole stripe width (64k * (num_drives - 1)) it has to > > first read a whole stripe (num_drives-1), calculate the parity, and > > then write to 2 disks. > > Not really. It can recalculate parity for a single block using the > parity block, the new block, and the block it is about to overwrite, > regardless of how many disks are in the stripe. > > In any case, RAID 5 (and even RAID 6) implementations are extremely fast > nowadays. What you should do is ask your database vendor what numbers > they expect in terms of read and write bandwidth and IOPS in order to > achieve your performance objective, and then use iozone or similar tools > to benchmark the RAID configurations you are considering. > > Note that using direct I/O and/or asynchronous I/O may have a large > impact on performance, as well as available memory. The RAID level may > be essentially insignificant compared to these factors. Just try to make > your RAID block size equal to the database block size. And align your > partitions to the block size as well, or don't use partitions at all. > See this essay for further info on the latter: > > http://insights.oetiker.ch/linux/raidoptimization/ > > _______________________________________________ > Linux-PowerEdge mailing list > [email protected] > https://lists.us.dell.com/mailman/listinfo/linux-poweredge > Please read the FAQ at http://lists.us.dell.com/faq _______________________________________________ Linux-PowerEdge mailing list [email protected] https://lists.us.dell.com/mailman/listinfo/linux-poweredge Please read the FAQ at http://lists.us.dell.com/faq
