Hi,

 

RAID 10 and/or RAID 50 will probably beat RAID5 for read access speeds.  This is where you add striping to RAID.  Double the disks are needed though, which may not be practical for every situation.

 

Personally, I am not a big fan of RAID5 at all.  The big "advantages" of RAID5 are supposedly that (a) it is more robust because you have 3 drives and if any one of them fails, the other two will carry on and (b) it is more space efficient.  In my experience part (a) is false too often for comfort and part (b) is true but not a strong advantage.

 

For RAID5 robustness, what happens in reality is as follows:  One drive fails.  RAID continues working in degraded mode as advertized.  System admin goes to replace the failed drive.  So far so good.  Soon as he pulls out the failed drive, I have seen on more than one occasion, that either due to RAID controller fault or administrator error, the wrong drive was pulled and/or one of the remaining drives or the RAID array got corrupted, so now you have accidentally blown away the entire volume with no hope of recovery, in a few seconds.  In contrast, I have never observed RAID1 controllers to fail this way.

 

Furthermore, It is also very easy to clone a RAID1 volume simply by removing one of the two volumes and replacing with a blank one and re-generating the RAID1 array, e.g. if you want to make a secobd server identical to the first.  This is not possible to do with RAID5.

 

With drive costs going lower all the time, I do not see RAID5 as a big advantage really as far as space efficiency.  Hence I usually go with RAID1 or RAID10 unless the client insists on RAID5 or RAID50 and the client is always right of course :-)

 

Just wondering if anyone else has experienced the same.

 

JW

 

 

On 10/26/07, Patrick <london31uk@xxxxxxxxx> wrote:

John,

 

Thanks for your very clear insight to best storage solution for exchange. Just to add a bit and get a little more clarification.

 

Would it not be best to have OS and Trans Logs on Raid 1 and DB on Raid 5? would that not be a better solution for the read and write issue?

 

According to an MS publication I once read, they recommend you have Trans Logs and DB's on different physical disks, and if you decide to implement storage groups, you are adviced to have each storage group and trans logs on different partitions as well. Just wondering how one can achieve that without your exchange implementation being extremely expensive.

 

 

----- Original Message ----
From: John T (lists) < johnlist@xxxxxxxxxxxxxxxxxxx>
To: exchangelist@xxxxxxxxxxxxx
Sent: Wednesday, October 24, 2007 11:38:52 PM
Subject: [ExchangeList] Re: Exchange 2003 disk partition'g question

Responding on list as it is good information for all.

 

Each type of RAID has goods and bads. The downside to RAID5 is it is slower on writes, as it must not only decide where to put the data but also must calculate and then write the checksum on the x drive. However, nothing can beat RAID5 on reads.

 

While I understand your concern about drive space overhead, you have to take a look at the larger picture. In your information, you state the server is also going to be a file server. If at all possible, I would suggest using a different server for that, or using an external storage device such as one that has 4 drives and is configured as RAID5 so the OS only sees the virtual drive.

 

Getting back to Exchange, there is a lot of writing going on, both to the Exchange DB files as well as the transaction logs, therefore they are both better suited to be on RAID1 sets. Same thing with your page file partition, a lot of writing and reading is done there.

 

For a partition holding files for storage, there is not a lot of writing going on so RAID5 is fine. Same thing with a SQL database. The Database writing is done in chunks, where is most of the IO is reads, so SQL databases are often on RAID5, but the transaction logs are never on RAID5.

 

John T

 

From: Jason Davis [mailto:JDavis@xxxxxxxxxx ]
Sent: Wednesday, October 24, 2007 3:22 PM
To: 'johnlist@xxxxxxxxxxxxxxxxxxx '
Subject: RE: [ExchangeList] Re: Exchange 2003 disk partition'g question

 

Hi John,

 

Please forgive my ignorance....

 

I was reading your email regarding Exchange Server fault-tolerant recommendations.  What is the reason for 4 physical drives in 2 RAID-1 sets?  Currently, we are building a new Exchange Server which contains 4, 150GB drives.  We were planning on using RAID-5 whereby we would have a total of 450GB free disk space (since we would effectively lose the 1 drive due to striping).  If we go with 2 RAID-1 sets, we are down to 300GB free disk space...... Keep in mind that we want to use this as a File Server in addition to an Exchange Server.  Is that recommended?  How do you feel about us implementing RAID-5 instead?

 

Thanks for your time!

 

(I hope you don't mind me emailing you directly)

 

--Jason Davis

 

---

From: John T (lists) [mailto: johnlist@xxxxxxxxxxxxxxxxxxx]

Sent: Wednesday, October 24, 2007 2:35 PM
To: exchangelist@xxxxxxxxxxxxx
Subject: [ExchangeList] Re: Exchange 2003 disk partition'g question

 

For an Exchange server, recommendation is minimum 4 physical drives in 2 RAID1 sets.

 

First RAID1 set: OS partition, Page file partition, Logs partition

Second RAID1 set: Exchange DB partition, Backup partition

 

John T

 

From: exchangelist-bounce@xxxxxxxxxxxxx [mailto:exchangelist-bounce@xxxxxxxxxxxxx] On Behalf Of Todd Lemmiksoo
Sent: Wednesday, October 24, 2007 2:23 PM
To: 'exchangelist@xxxxxxxxxxxxx '
Subject: [ExchangeList] Re: Exchange 2003 disk partition'g question

 

Yes, raid 1 = 2 physical drives.

 

---

From: exchangelist-bounce@xxxxxxxxxxxxx [mailto:exchangelist-bounce@xxxxxxxxxxxxx] On Behalf Of Michael B. Smith
Sent: Wednesday, October 24, 2007 4:40 PM
To: exchangelist@xxxxxxxxxxxxx
Subject: [ExchangeList] Re: Exchange 2003 disk partition'g question

You have a SINGLE 73 GB drive?

 

From: exchangelist-bounce@xxxxxxxxxxxxx [mailto:exchangelist-bounce@xxxxxxxxxxxxx] On Behalf Of Todd Lemmiksoo
Sent: Wednesday, October 24, 2007 4:22 PM
To: exchangelist@xxxxxxxxxxxxx
Subject: [ExchangeList] Exchange 2003 disk partition'g question

 

I will be migrating my Exchange 5.5 org to Exchange 2003 in the near future. (Thanksgiving weekend) And am asking for disk drive partitioning suggestions. Our current Exchange org is taking about 15 Gb of disk space on an NT4 server. I have a 73 Gb drive that I am planning on using for the Exchange 2003 setup. What size partitions should I build for the migration?

Todd Lemmiksoo
Network Administrator

All-Mode Communications, Inc.
1725 Dryden Road
Freeville, New York  13068
(607) 347-4164 x440
1-877-ALLMODE  (toll free)
http://www.all-mode.com

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