Date: Fri, 24 Sep 1999 11:01:44 +0930 From: Greg Lehey <grog@lemis.com> To: Douglas Anderson <AndersonD@MTA.NET> Cc: FreeBSD Questions <questions@FreeBSD.org> Subject: Re: vinum raid 1... Message-ID: <19990924110144.M53220@freebie.lemis.com> In-Reply-To: <48506CC52C52D3119B4300508B0903B514B5E5@EXCHANGE10>; from Anderson, Douglas on Thu, Sep 23, 1999 at 01:04:11PM -0700 References: <48506CC52C52D3119B4300508B0903B514B5E5@EXCHANGE10>
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On Thursday, 23 September 1999 at 13:04:11 -0700, Douglas Anderson wrote: > In a two (physical) drive mirrored system what would be the impact of > putting each drive on its own scsi channel when using a two channel scsi u2 > controller? Very little. > Would this reduce or eliminate the write bandwidth penalty? No. > Again, assuming the same setup - would vinum just alternate drives on > successive reads or... or can vinum read concurrently from both drives? Vinum can read concurrently from both drives. What it does depends on what you ask it to do. And you do that by reading or writing, which doesn't give you or Vinum much control over where the data is. In a "pure" RAID-1 configuration (two plexes, each with one subdisk on a different drive), Vinum will read alternately from one drive, then the other. > I am attempting to decide whether to implement mirroring or simply > split data files and system/swap files between drives. Space is not > an issue. I have mild concerns regarding redundancy but want to > minimize performance losses in a small system which will employ a > SQL server with a moderate size database. Reads/writes will occur on > a 98%/2% ratio but relational joins will occur continuously. Writing to RAID-1 is a little slower than writing to a single plex, but not as much as you would think. Take a look at the graphs at http://www.lemis.com/vinum/Performance-issues.html for more details. For better performance, you might like to stripe the plexes. You can still do this with 2 disks; just ensure that the first subdisk in each plex is on a different disk. Greg -- When replying to this message, please copy the original recipients. For more information, see http://www.lemis.com/questions.html See complete headers for address, home page and phone numbers finger grog@lemis.com for PGP public key To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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