Anthony: >From real world experience, I have seen Exchange work fine with Exchange using LUN's carved out of a RAID group shared with other hosts doing significant I/O. I have seen it not work right, even when its LUN's were on dedicated, separate RAID groups, because the LUN's were assigned to a controller that was overloaded (although the impact on exchange was minimal compared to the impact on the file server which was in the same boat).
Lots of factors go in to the performance of a SAN, but from my experience (with Hitachi Data Systems/Brocade based SAN's) the RAID group the LUN's are physically on are of almost no importance. More important is that (in a SAN with multiple controllers, and you'd be foolish to even consider one which didn't have multiple controllers), the LUN's be distributed properly (in most SAN architectures, LUN's are assigned to one default controller or another, and use that unless there is a problem with it, so if you screw up and put all of your high I/O LUN's on one, you WILL see horrible horrible problems). HDS has a good paper on RAID 5 vs. RAID 1 for exchange; some of the info is specific to HDS equipment, but some of it is pretty generally true: http://www.hds.com/pdf/wp_144_exchange2000_9570v.pdf#view=FitH&pagemode=book marks Honestly, the theory can be argued until we are all blue in the face, but you should simply test out your configuration anyways. You may find that dedicating RAID groups is necessary, but I doubt it. The bottleneck will be the controllers on the disk array, not the physicaly seek time of the HDD's, so the proper LUN assignment (which does require design) is crucial. Also, making sure you don't overload any particular path (which involves switch load, the port on the disk subsystem controllers the switches are connected to, cache size -- most disk controllers have insane amounts of cache on them, but you never want less cache :-)). My $.02; I'd be happy to share more if you have specific questions. > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Behalf Of > Anthony Sollars > Sent: Monday, April 19, 2004 11:01 PM > To: Exchange Discussions > Subject: RE: Exchange 2k3 & SANs > > > Then why oh why does very Exchange documentation out there > and every Vendor > we have spoke with support the idea that you need to design > design design > your disk subsystem for exchange. This goes as far to say they highly > recommend dedicating spindles only to exchange. We are > planning on running > 5000 users off this SAN across 2-3 Exchange servers, we just > don't buy the > idea of let it ride across and disks and it will be fine. We > have started to > develop some jet stress testing, I will let you know how it > goes. If anyone > has real world experiences to share please I would love to hear them, > theories are welcome but may be sent to /dev/null :P. > > -Tony > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of Ed > Crowley [MVP] > Sent: Sunday, April 18, 2004 11:02 AM > To: Exchange Discussions > Subject: RE: Exchange 2k3 & SANs > > The RAID type you use for a single set of logs is unimportant > because the > log volume is almost entirely a sequential write, so there is > very little > seek time. A RAID-1 pair for a single set of logs should be > sufficient for > any number of Exchange users. Again, separating SAN drives > into physical > groups just to support Exchange is overly costly. If you > configure the SAN > as it should be configured, i.e., a "sea of drives", then you > will want to > work with your SAN engineer to ensure that the the SAN will be able to > sustain the necessary data rates of your particular Exchange > infrastructure. > > Ed Crowley MCSE+Internet MVP > Freelance E-Mail Philosopher > Protecting the world from PSTs and Bricked Backups!T > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On > Behalf Of Jon Hill > Sent: Sunday, April 18, 2004 8:58 AM > To: Exchange Discussions > Subject: RE: Exchange 2k3 & SANs > > Let's say you have 200GB of database and 75GB of daily logs. > You will get > better performance if you stripe both "disks" across five > RAID groups than > if you put the db on one and the logs on another. > > We have an HP XP-512, a storage frame comparable to (and IMHO > better than) > whatever model of Symmetrix was being sold in the last months > of 2001. Our > initial disk layout for Exchange 2000 was very badly designed > (gotta love > VARs), with the db and logs sharing a single RAID group. I > recently took it > upon myself to mitigate the design problem by moving the logs > to another > part of the frame but I did not detect any improvement in > performance. > > Of course, it could be that we're just not hitting the server > hard enough > for disk I/O to be a problem. In certain limited situations, yes it's > better to separate the db LUNs from the log LUNs, but to optimize > performance you need to consider what else is on these spindles, disk > controllers, ports and port controllers (in XP terms, the > parity groups, > ACPs, ports and CHIPs), not to mention cache. For example, > if you have an > I/O-intensive Oracle app on the same ports as Exchange, you > may find that > the port becomes a bottleneck regardless of where the Oracle > data is stored. > These are the kinds of things your SAN administrators will > consider when > allocating disk space. Unless you have reason to doubt them, > trust the SAN > admins to know what they're doing. > > > -----Original Message----- > From: Anthony Sollars [mailto:[EMAIL PROTECTED] > Sent: Friday, April 16, 2004 2:00 PM > To: Exchange Discussions > Subject: Exchange 2k3 & SANs > > > Does anyone on the list have Exchange 2k3/2k running on an > EMC SAN or other > comparable SAN product. We are getting a lot of push back > from the SAN group > because we want to design our disk layout for optimum I/O > performance and > have dedicated spindles for Exchange, and they don't feel it > is necessary. > Do any of you have any real world experience with the pains > of not designing > your SAN I/O properly and not following Vendor/MS best > practices with disk > configuration? Thanks for the input, we are planning on > engaging EMC and > performing some tests like these in there labs, but would > like to get some > real world experiences from all of you. > > Anthony Sollars > Sr. Technology Consultant > PACCAR Inc > > > _________________________________________________________________ > List posting FAQ: http://www.swinc.com/resource/exch_faq.htm > Web Interface: > http://intm-dl.sparklist.com/cgi-bin/lyris.pl?enter=exchange&t ext_mode=&lang =english To unsubscribe: mailto:[EMAIL PROTECTED] Exchange List admin: [EMAIL PROTECTED] To unsubscribe via postal mail, please contact us at: Jupitermedia Corp. 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