Re: [IMail Forum] New Server Specs

Thu, 23 Feb 2006 14:22:47 -0800

John,

It would be good to stop saying this.  In real-world scenarios where redundancy is necessary, RAID 5 is the best for performance when you have between 3 and 6 drives.  RAID 50 becomes better once you get to 8 drives.

The issue is that while spanning has less overhead, it negatively impacts fault tolerance.  Even with RAID 10 and 6 drives, RAID 5 would still outperform with the same number of drives.  Generally speaking RAID 5 with 6 drives reads at about the same speed of 5 spanned drives, and writes at about the speed of 4 spanned drives.  If you took those same 6 drives and made them RAID 10, they would read and write like 3 spanned drives.  RAID 5 also would give you about 70% more disk space in this setup.

There is more to this story as well.  Because E-mail is mostly under the stripe size of the drives, files in the spool mostly only get written to one drive.  In this case there is no read or write performance gain for a single file among RAID 10 or RAID 5, but when a system is busy and you can write to one of 5 drives instead of one of 3 drives, there is more of a chance of having an inactive disk handle the work.  So again RAID 5 is superior.

There is absolutely no doubt that when you have between 3 and 6 disks that RAID 5 is superior unless you have no interest in redundancy, and for a mail server, we all should have redundancy.

Note that newer cards supporting RAID 6 is a good alternative to RAID 5 if you want to run a hot spare.  If you don't want a hot spare, I would stick to RAID 5.

Matt



John T (Lists) wrote:

Sorry, make that Raid5 is poor on write.

 

It is great on read.

 

Spool and mailboxes have a lot of write activity.

 

John T

eServices For You

 

"Seek, and ye shall find!"

 

-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of John T (Lists)
Sent: Thursday, February 23, 2006 12:57 PM
To: [email protected]
Subject: RE: [IMail Forum] New Server Specs

 

For spool and mail boxes, faster is better.

 

Do not user Raid5 for spool or mail boxes. Raid5 is poor on read.

 

Search the archives. There has been a lot of discussion about this in the past.

 

John T

eServices For You

 

"Seek, and ye shall find!"

 

-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of Jim F.
Sent: Thursday, February 23, 2006 12:13 PM
To: [email protected]
Subject: [IMail Forum] New Server Specs

 

Hello All:

 

I haven't gotten any responses to any of my other questions that I've sent to the group, hopefully this one will.

 

I'm trying to spec out a new server and had a question for the group in regard to HDD configuration.  What kind of RAID setup works best on a mid-size Imail installation?  Is RAID-1 acceptable or is RAID-5 recommended? Also, would 15K RPM disks make a huge difference as opposed to 10K RPM disks?

 

Thanks,

Jim Frasch

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