Thanks, everyone. I got some excellent replies, including some long 
explanations. Appreciate the time you guys took out for the responses.
The gist of it i take, is to use RAID10. I have 400MB+ of write cache on the 
controller(s), that the RAID5 LUN(s) could benefit from by filling it up and 
writing out the complete stripe, but come to think of it, it's shared among the 
two Storage Processors, all the LUNs, not just the ones holding the pg_xlog 
directory. The other thing (with Clariion) is the write cache mirroring. Write 
isn't signalled complete to the host until the cache content is mirrored across 
the other SP (and vice-versa), which is a good thing, but this operation could 
potentially become a bottleneck with very high load on the SPs.
Also, one would have to fully trust the controller/manufacturer's claim on 
signalling the write completion. And, performance is a priority over the drive 
space lost in RAID10 for me.
I can use 4 drives instead of 6.

        t-----Original Message----- 
        From: Gregory S. Williamson [mailto:[EMAIL PROTECTED] 
        Sent: Tue 8/16/2005 6:22 PM 
        To: Anjan Dave; 
        Subject: RE: [PERFORM] choosing RAID level for xlogs

        I would be very cautious about ever using RAID5, despite manufacturers' 
claims to the contrary. The link below is authored by a very knowledgable 
fellow whose posts I know (and trust) from Informix land.


        Greg Williamson 
        GlobeXplorer LLC 

        -----Original Message----- 
        From:   [EMAIL PROTECTED] on behalf of Anjan Dave 
        Sent:   Mon 8/15/2005 1:35 PM 
        Subject:        [PERFORM] choosing RAID level for xlogs 


        One simple question. For 125 or more checkpoint segments 
        (checkpoint_timeout is 600 seconds, shared_buffers are at 21760 or 
        170MB) on a very busy database, what is more suitable, a separate 6 
        RAID5 volume, or a RAID10 volume? Databases will be on separate 
        spindles. Disks are 36GB 15KRPM, 2Gb Fiber Channel. Performance is 
        paramount, but I don't want to use RAID0. 


        PG7.4.7 on RHAS 4.0 


        I can provide more info if needed. 


        Appreciate some recommendations! 





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