Re: Hardware Recommendations
- From: "John Fullbright" <Fullbrij@xxxxxxxxxxx>
- Date: Thu, 12 Jan 2006 16:47:22 -0500
I don't understand what you're talking about when you say " but I would
expect to be given my pink slip if I recommended it as a customer solution
for a Database due to
the lack of redundancy and high risk we would assume."
RAID 1 is 100% redundant, it's mirroring..
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"
Exchange databases are a random workload that uses a 4K (small requests) IO
size. A three drive RAID 5 set uses more spindes at higher cost and
provides lower performance than a mirror. I don't see where any of the
criteria are met for a RAID 5 recommendation.
The same paper discusses the characteristics of RAID 1/0+1/10:
" · Performance:
For write requests, both parts of a mirror must be updated, reducing
the available write throughput by >50% for 2-way mirrors, >66% for 3-way
mirrors, and so on. On the other hand, read performance improves as
the number of mirrors in each set increases.
· Reliability:
For an M-way mirrored set, all M disks must be lost before data is lost. In
the common case of a simple 2-way mirror, MTBF is now increased because it
is the longer of two semi-independent disk lifetimes. In most cases, the
mirror can be restored quickly (for example, by replacing the disk by hand
or using a hot spare), further reducing the window of vulnerability. For
non-trivial mirrored striped arrays, most multi-disk failures are
survivable.
· Availability:
If connectivity is lost to one disk, or even M-1 disks of every M-mirrored
set in a striped array, work can still proceed, albeit at a different level
of throughput; failure of a mirror spindle decreases read performance and
increases write performance for that set. When disconnected disks become
reachable again, they can be synchronized back to the corresponding active
disks, thereby restoring the original array characteristics."
Both a RAID 5 set with 3 disks and a Mirror can withstand the failure of a
single drive. I'm not seeing a redundancy problem that would result in a
pink slip here. I do see a potential perfrormance problem with RAID 5 that
could however result in that pink slip.
"Jonathan Norris" <JonathanNorris@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in
message news:896AC5A6-9D41-412C-8498-265B7D2A11AB@xxxxxxxxxxxxxxxx
>I am using a calculator developed by Exchange Rangers and have used it
> without any issues (both theoretically and in the real world) It uses the
> same calculations as John Fullbright had illustrated with more
> considerations.
>
> I ran the information you provided, if you can provide your average
> mailbox
> size, User Concurrency, Disk Size, Disk RPMs, I will rerun it and give you
> the projections.
>
> Interesting enough it doesn't even provide recommendations for RAID1 on
> the
> DB spindles.
>
> Agreed Raid 1 does provide more performance, but I would expect to be
> given
> my pink slip if I recommended it as a customer solution for a Database due
> to
> the lack of redundancy and high risk we would assume.
>
> Unless your users have a really high IOP Profile or really huge mailboxes
> I
> wouldn't expect RAID 5 to be a bottleneck (unless you have your OS and
> Transaction Logs sitting on the same Disks/spindles). Which isn't Best
> Practice or Recommended by anyone I know (With all due respect).
>
> You may also consider running Microsoft Best Practice Analyser to see if
> it
> gives you any recommendations. Perhaps you have write cache enabled on
> the
> drives?
>
> I would also recommend you run performance monitor to see what the
> bottleneck is before you spend money.
>
> Here is a link you may want to check out for Troubleshooting Performance
> with Exchange.
>
> http://www.microsoft.com/technet/prodtechnol/exchange/2003/library/e2k3perf.mspx
>
> --
> Jonathan
> No Warrenties Implied, Did you do a FULL backup today??????
>
>
>
>
> "Asher_N" wrote:
>
>> Another one of my pet peeves. Similar to the old, 'the arrow will never
>> reach the target' problem. While your number are sound, any decent RAID
>> controller has on-board cache. writes are cached and delayed until read
>> are satisfied.
>>
>> So while the theorical problem points to fsaster writes with mirror, if
>> you use the same drives and same RAID controler to do R1 or R5, you
>> should get similar results. Also, 150 users is not much. I run 100 users
>> on a single 5 drive partitioned as 2 logical drives (OS, Stores and
>> logs). The performance is more than adequate.
>>
>> "John Fullbright" <Fullbrij@xxxxxxxxxxx> wrote in
>> news:#eQkfp6FGHA.3936@xxxxxxxxxxxxxxxxxxxx:
>>
>> > I wouldn't do that, "three disks in RAID 5 for the Database .STM and
>> > .EDB Files it would be 7 Disks.", that is.
>> >
>> > Let's assume a 3:1 read/write ratio for tha deatabases. We'll also
>> > assume 10K RPM SCSI disks which are capable of ~85 20ms IOPS.
>> >
>> > Where P is the performance of a single spindle and N' is the number of
>> > data spindles in the set:
>> >
>> > RAID 5 Read performance = P*N' = 85*2 = 170
>> > RAID 5 Write performance =P*N'/4 = 85*2/4 = 42.5
>> >
>> > And we apply the read/write raitio which is required when read and
>> > write performance are asymmetrical. With a 3:1 ratio we are 75% read
>> > and 25% write:
>> >
>> > Performance = 170*.75 + 42.5*.25 =127.5+10.625 =138.125 IOPS
>> >
>> > If you were to buy bigger drives and go with just a mirror:
>> >
>> > RAID 1 Read performance = P*N = 170
>> > RAID 1 Write performance = P*N/2 = 85
>> >
>> > Again we apply the read/write ratio:
>> >
>> > 170*.75 + 85*.25 = 127.5 + 21.3125 = 148.8125 IOPS
>> >
>> > My recommendation - Three mirrors for a total of 6 spindles. This is
>> > about 8% better overall performance on the database array with 1 fewer
>> > spindles. The write performance is a 100% improvement.
>> >
>> > Do the math.
>> >
>> > John
>> >
>> >
>> >
>> >
>> >
>> > "Jonathan Norris" <JonathanNorris@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in
>> > message news:D662866D-5331-4A4A-8B48-7EF998ABE340@xxxxxxxxxxxxxxxx
>> >> Actually if i were to use two Disks for the OS (Raid 1) and two Disks
>> >> for Transaction Logs (Raid 1) and three disks in RAID 5 for the
>> >> Database .STM and
>> >> .EDB Files it would be 7 Disks.
>> >>
>> >> Also keep in mind by having everything on the same spindles you will
>> >> have an
>> >> I/O bottleneck.
>> >>
>> >> OS/Page File is Read and Write intensive
>> >> Transaction Logs are write intensive during normal operation and
>> >> during recovery its read intensive.
>> >> DB File .stm and .edb are both Read and Write Intensive.
>> >>
>> >>
>> >> --
>> >> Jonathan
>> >> No Warrenties Implied, Did you do a FULL backup today??????
>> >>
>> >>
>> >>
>> >>
>> >> "Ryan Burrus" wrote:
>> >>
>> >>> I am trying to find some information as to the recommended hardware
>> >>> configuration for Exchange Server 2003. We only have about 150
>> >>> users and all
>> >>> access it using Outlook 2003. I have read a few things from
>> >>> Microsoft that
>> >>> says the Exchange data files and the page file should be on separate
>> >>> drives.
>> >>> Also that the Exchange data files and the Windows system files
>> >>> should be on
>> >>> separate drives. Also that the Exchange transaction logs should be
>> >>> on a separate drive than the Exchange data files. This would equate
>> >>> to 4 drives
>> >>> which doesn't sound right to me. Does anyone know what the
>> >>> recommended scenario would be for an organization our size? Any
>> >>> advice would be much appreciated. Thanks!!
>> >
>> >
>> >
>>
>>
.
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