RAID1 vs RAID10?
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From: Mark Arnold [MVP] on 13 Jan 2006 08:39 On Fri, 13 Jan 2006 04:50:31 -0500, "Hank Arnold" <rasilon(a)aol.com> wrote: >Sure you can.... There is a cage that can be added that will convert the 2 >external drive bays into a 3rd RAID array. It will require that the bays be >empty and adding at least one more RAID adapter. We configured this for our >2 ML370 servers until we decided to go with new hardware..... Hank, Have they changed the internal architecture? Last time I had a 370 in my hands, which was a long time ago since, the stack of 6 was connected via backplane to a single controller cable. How could you do RAID10 on any more than 2 disks?
From: John Fullbright on 13 Jan 2006 10:45 I wouldn't go with RAID 5. The Microsoft Whitepaper "Disk Subsystem Performance Analysis for Windows" gives a set of criteria where it is appropriate to use RAID 5. http://download.microsoft.com/download/e/b/a/eba1050f-a31d-436b-9281-92cdfeae4b45/subsys_perf.doc#_Toc72126973 Quoting from the paper: "RAID-5 might be the right choice for a write-heavy workload if the following is true: ? The workload consists of large requests in comparison to the array's stripe unit size (that is, they constitute several complete stripes of data on average), or the controller has a write-back cache, allowing writes to be delayed and coalesced into full stripes, and ? The workload is largely sequential (in terms of LBNs), and ? The array controller can detect and optimize for full stripe writes, and ? The number of spindles is reasonable, as described in "Rules of Thumb" later in this paper, and ? Cost is a serious issue" Since we were talking the same number of spindles in either case, RAID 5 for exchange meets none of these criteria. 1&2. An Exchange DB workload consists of random small (4K) IOs. 3. You'll be hard pressed to find a controller that can optimize full stripe writes. Even if you do, the small size of the RAID 5 set proposed would negate any benefit. 4. The spindle count in the proposed RAID 5 set is too low to meet the rule of thumb mentioned. 5. Since we are talking the same number of spindles, there is no cost advantage to going RAID 5. John "Hank Arnold" <rasilon(a)aol.com> wrote in message news:uTNXTgCGGHA.1100(a)TK2MSFTNGP10.phx.gbl... >I like the second proposal better if you dump the "hot spare" and go with >RAID 5. > > Actually, what I would do is dump the 300GB drive and add another 146GB > drive. Make the configuration > > 2 x 72GB RAID 1 OS > 2 x 146GB RAID 1 Logs > 4 x 146GB RAID 10 Databases > (or RAID 5 w/ hot spare) > > This assumes that there is room for the NTBACKUP file somewhere on one of > the drives or putting it somewhere on another network drive.... > > As others have said, this is hard to specify w/o doing an analysis of > usage. Check out MS articles. Also, look for some Exchange configurators > (I believe Dell has one) that will walk you through the anticipated setup > and usage and recommend hardware.... > > -- > Regards, > Hank Arnold > > "Paul Hutchings" <paul(a)spamcop.net> wrote in message > news:paul-EFCC7A.21583512012006(a)msnews.microsoft.com... >> I'm planning on getting an ML370 to support approx 600 mailboxes (huge >> variation of size and usage profiles). >> >> I was planning on this: >> >> 2 x 72gb 15k SCSI hardware RAID1 on Channel A partitioned for OS + Logs >> 4 x 146gb 10k SCSI hardware RAID10 on Channel B for first storage group >> and database (still reading up but can't envisage more than 1 >> SG/database). >> 1 x 146gb 10k SCSI hot-spare. >> 1 x 300gb 10k SCSI spindle for NT backup to disk (to then be streamed to >> tape). >> >> I wanted some opinions/thoughts on whether I would be better off >> considering: >> >> 2 x 36gb 15k SCSI hardware RAID1 on Channel A for OS >> 2 x 36gb 15k SCSI hardware RAID1 on Channel B for Logs >> 2 x 146gb 10k SCSI hardware RAID1 on Channel B for first storage group >> and database (seems MS now say RAID1 over RAID5). >> 1 x 146gb 10k SCSI hot-spare. >> 1 x 300gb 10k SCSI spindle for backup >> >> The server will likely be a dual 3.4ghz 2mb cache Xeon with 4gb RAM. >> >> I'm aiming to avoid an external storage cabinet for now, but this way >> the option is still there in the future if needed. >> >> Basically I've been reading way too much and I suspect I'm getting a >> little "performance paranoid" where for our sort of usage either will do >> the job. >> >> cheers, >> Paul >> -- >> paul(a)spamcop.net > >
From: Paul Hutchings on 13 Jan 2006 12:37 In article <99bfs1hpgehd341ieia37thlhac1aphdf9(a)4ax.com>, "Mark Arnold [MVP]" <mark(a)mvps.org> wrote: > Hank, Have they changed the internal architecture? Last time I had a > 370 in my hands, which was a long time ago since, the stack of 6 was > connected via backplane to a single controller cable. > How could you do RAID10 on any more than 2 disks? There is, by default, a single six bay backplane. One option is to get a split backplane which gives a 2/4 split. Another option is to get a two-drive cage that goes in below the CD drive - this has its own backplane. So with a 6402 SmartArray you can have Channel A connected to the two-drive cage backplane for the RAID1 boot/log pair, and Channel B connected to the six bay backplane for the main RAID10 plus the backup spindle. I guess if you needed it you could combine the two with a four channel RAID controller and have three channels. At the moment I am planning on going with "option A" but having a 73gb 15k mirror for the OS/logs instead of 36gb. Having the logs on a separate controller channel should offset having dedicated drives but on the same backplane as the store. I believe going this way will do all that we need for now and the foreseeable future - if we find performance is a problem it's easy enough to add an enclosure and add disks, but it's possible we'll be looking at things such as SANs within the next 12 - 18 months so I'm hesitant to invest in drive cabinets right now unless they are 110% necessary. I downloaded the Dell Exchange 2003 sizer tool and even if you tell it there are a thousand heavy users it only suggests a PE2800 with 2gb ram and internal RAID5, sods law the HP website times out trying to get their sizer tool :-) Paul -- paul(a)spamcop.net
From: John Fullbright on 13 Jan 2006 15:18 "I downloaded the Dell Exchange 2003 sizer tool and even if you tell it there are a thousand heavy users it only suggests a PE2800 with 2gb ram and internal RAID5, sods law the HP website times out trying to get their sizer tool :-)" Wow, a thousand. Let's see.. the assumption for a heavy user, which in over 300 deployments in my experience has never been accurate, for a heavy user is .75 IOPS. Let's be generous and assume everyon is using cahced mode and we have a 2:1 read write ratio. Your limit would still be just under 200 users using the math in "Optimizing Storage for Exchange 2003". <PESSIMISM> Consider the source: Dell is trying to sell you hardware. Microsoft is trying to prevent support cases. Which would you trust? Sounds to me like and undersell, and Dell will go after the SAN sale in 12 months with a similarly undersize Clariion. Six months later, they'll follow up by recommending a bunch of additional shelves costing more than the original SAN purchase. </PESSIMISM> "Paul Hutchings" <paul(a)spamcop.net> wrote in message news:paul-A36CC9.17375613012006(a)msnews.microsoft.com... > In article <99bfs1hpgehd341ieia37thlhac1aphdf9(a)4ax.com>, > "Mark Arnold [MVP]" <mark(a)mvps.org> wrote: > >> Hank, Have they changed the internal architecture? Last time I had a >> 370 in my hands, which was a long time ago since, the stack of 6 was >> connected via backplane to a single controller cable. >> How could you do RAID10 on any more than 2 disks? > > There is, by default, a single six bay backplane. > > One option is to get a split backplane which gives a 2/4 split. > > Another option is to get a two-drive cage that goes in below the CD > drive - this has its own backplane. > > So with a 6402 SmartArray you can have Channel A connected to the > two-drive cage backplane for the RAID1 boot/log pair, and Channel B > connected to the six bay backplane for the main RAID10 plus the backup > spindle. > > I guess if you needed it you could combine the two with a four channel > RAID controller and have three channels. > > At the moment I am planning on going with "option A" but having a 73gb > 15k mirror for the OS/logs instead of 36gb. > > Having the logs on a separate controller channel should offset having > dedicated drives but on the same backplane as the store. > > I believe going this way will do all that we need for now and the > foreseeable future - if we find performance is a problem it's easy > enough to add an enclosure and add disks, but it's possible we'll be > looking at things such as SANs within the next 12 - 18 months so I'm > hesitant to invest in drive cabinets right now unless they are 110% > necessary. > > I downloaded the Dell Exchange 2003 sizer tool and even if you tell it > there are a thousand heavy users it only suggests a PE2800 with 2gb ram > and internal RAID5, sods law the HP website times out trying to get > their sizer tool :-) > > Paul > -- > paul(a)spamcop.net
From: Paul Hutchings on 13 Jan 2006 18:41
In article <#Txa74HGGHA.608(a)TK2MSFTNGP14.phx.gbl>, "John Fullbright" <Fullbrij(a)comcast.com> wrote: > Wow, a thousand. Let's see.. the assumption for a heavy user, which in over > 300 deployments in my experience has never been accurate, for a heavy user > is .75 IOPS. Let's be generous and assume everyon is using cahced mode and > we have a 2:1 read write ratio. Your limit would still be just under 200 > users using the math in "Optimizing Storage for Exchange 2003". John, thanks for all the info. I've been reading the "Calculate Your Server Size" document at Microsoft. Now if I'm understanding all this correctly, at it's most basic I should assume around 80 IOPS/Second per spindle on a RAID10 disk subsystem. This gives approx 320 IOPS/Second on a 4 spindle RAID10. If I assume that every single user (physical member of staff not mailboxes) who will be using this server is a "heavy user" I have around 400 staff at 0.75 IOPS/Second per user, so 400 x 0.75 = 300 IOPS/Second. That's if *everyone* is a heavy user, I guess it also assumes they all using the server at the same time (they don't) and it also assumes that Microsofts average of 0.75 for a heavy user is accurate. It seems to suggest that I'm speccing about right? Of those 400 staff I'd break it down as approx 200/100/100 if I were to try and say what the light/medium/heavy user split is (we have a lot of technicians and users who don't work at a desk and use mail all day). I'll do some digging and see how they suggest measuring/converting the load on the current 5.5 box to IOPS/Second per Mailbox so I can get a measurement rather than take an educated guess. Thanks again, Paul -- paul(a)spamcop.net |