The other point that is well made is that with enough drives you will max out the PCI bus before you max out the drives. 64-bit 66Mhz can do about 400MB/sec, which can be acheived by two 3 drive stripes (6 drive in RAID 10). A true PCI-X card can do better, but can your controller? Remember, U320 is only 320MB/channel...
Alex Turner NetEconomist On 8/16/05, Anjan Dave <[EMAIL PROTECTED]> wrote: > 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. > > Thanks, > Anjan > > t-----Original Message----- > From: Gregory S. Williamson [mailto:[EMAIL PROTECTED] > Sent: Tue 8/16/2005 6:22 PM > To: Anjan Dave; pgsql-performance@postgresql.org > Cc: > 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. > > <http://www.miracleas.com/BAARF/RAID5_versus_RAID10.txt> > > Greg Williamson > DBA > GlobeXplorer LLC > > > -----Original Message----- > From: [EMAIL PROTECTED] on behalf of Anjan Dave > Sent: Mon 8/15/2005 1:35 PM > To: pgsql-performance@postgresql.org > Cc: > Subject: [PERFORM] choosing RAID level for xlogs > Hi, > > > > 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 > disk > 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! > > > > Thanks, > > Anjan > > > > > --- > This email message and any included attachments constitute > confidential > and privileged information intended exclusively for the listed > addressee(s). If you are not the intended recipient, please notify > Vantage by immediately telephoning 215-579-8390, extension 1158. In > addition, please reply to this message confirming your receipt of the > same in error. A copy of your email reply can also be sent to > [EMAIL PROTECTED] Please do not disclose, copy, distribute or take > any action in reliance on the contents of this information. Kindly > destroy all copies of this message and any attachments. Any other use > of > this email is prohibited. Thank you for your cooperation. For more > information about Vantage, please visit our website at > http://www.vantage.com <http://www.vantage.com/> . > --- > > > > > > !DSPAM:4300fd35105094125621296! > > > > > ---------------------------(end of broadcast)--------------------------- > TIP 9: In versions below 8.0, the planner will ignore your desire to > choose an index scan if your joining column's datatypes do not > match > ---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
