Raid 5 and Number of Drives

[billy437]

I am setting up new servers and I was reading the release notes on the 5.1 U1 and it gave examples of supported raid.

I was planning on installing 8 1TB drives and setting them up RAID 5.  The release notes says that they support the following examples.  It says 7 1TB drives in that note.

Is this just an example or if I use 8 drives will my server explode?  It just seems weird that I can use 7 but not 8 rather than a set rule of max number drives in a particular RAID type statement.

Anyone have any insight into this or do I have to burn a support call.

[weinstein5]

It has to do with the SCSI addressing - depending on the SCSI bus because some only have 8 addresses available - one is taken by the SCSI card leaving 7 available for drives - from Google -

On SCSI parallel buses the number of ids is related to the width. 8 bit buses (sometimes called "narrow") can have 8 SCSI ids of which 1 is taken by the HBA leaving 7 for SCSI devices. Wide SCSI buses are 16 bits wide and can have a maximum of 15 SCSI devices (targets) attached. The SCSI 3 draft standard allows a large number of ids to be present on a SCSI bus.

[billy437]

Thank you very much.  You know that actually makes sense.  So no big deal I guess I will go with the 7 as opposed to 8.  Do you have any opinion on the RAID type.  I have seen so many different opinions about raid 5 vs raid 6 vs raid 10.

[Kahonu84]

It really depends on what's going on the drives. Will there be a SAN?

[billy437]

It is local storage.  Can't afford SAN.  We have 2 drives Raid 1 for ESXi.

Then 8 1TB drives for data on each server.  We plan to use the Storage appliance.  The VMs are standard Windows 8 R2 running Exchange 2010 and print and file sharing, and SharePoint.

I have seen that there is better performance on the raid 10 so I might go that way but the HP servers need additional license to get that option.

Thanks for your help.

[weinstein5]

I would go RAID 5 - provides decent performance for most applications -

Also with you SCSI are able to enable the Wide SCSI bus this will allow you to use all 8 drives -

[billy437]

Thanks.  I am just so afraid of setting this up and it not performing well.

[Kahonu84]

Performance anxiety??

[billy437]

Ha funny!

[Josh26]

Poorly performing RAID is nearly always the result of a cheap RAID card, the lack of a battery backed cache, or too small a cache.

These issues have exponentially more impact than the RAID level.

Edit:

I have seen that there is better performance on the raid 10 so I might go that way but the HP servers need additional license to get that option.

This is not a licensed feature and you can choose to do so. However, if you require performance at a high enough level that you need to go down this path, the Storage Appliance is unlikely to be usable to you.