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Raid 5 initialization time

Phoenix86

Phoenix86

Lifer
Hey everyone, we are looking to upgrade our mail server capacity. Currently have 3x320gb (sata 2 2.5in 7200rpm) in raid 5, and we're going to upgrade these to 6x500gb.

Hardware is a dell power edge 2970 8gb RAM, perc 6i controller.

This is a little out of my scope of my normal duties but hey this is what you get when you hire a PC tech to manage servers too... Anyways Dell is estimating 5min/GB for the drives to initialization on the array which is 208 HOURS. This seems extremely... Incorrect.

Does anyone have a good method for initializing drive times or have some direct experience so I can propose a more reasonable estimate?
 
depends on the controller and the number of drives. Though I did have a highpoint 2xxx controller take 48 hours to just add a extra drive.

On the upside, a good controller will still have the drives online during the change over. So ig you have enough spare connectors, adding in the new drives, setting them up, then moving the data across will proberly result in the best up time.

Of course, if you do not have the needed extra connectors, then backing up, and replacing will take a little while to initilize the array. Actual time will vary (assuming no issues with the new drives) but then it is possible (if needed, but not the most wise option) to create the array, boot and use it, then leaving the complete initilization to occur in the back ground. Down side is that you are running without any raid protection and any changes made during this time will be lost if the array fails (or a power outtage occurs if your controller does not have a BBU or the system does not have a UPS.

Side note, as you are going to 6 drives, are you sticking with raid 5 or moving to raid 6 or a combination raid? (ie: 10 ) Much longer time IIRC for RAID6 over raid 5.
 
Im not sure I would want my exchange data on 500GB disks in Raid 5, that is a long rebuild time and Raid 5 in my experience is safer on smaller capacity drives....especially as you are dealing with physical rather than virtual. I would be tempted to use RAID 10 instead..

Some reading for you...the article is old, but more relevant now due to disk size!

why Raid 5 stops working
 
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Thanks for the replies.

We are looking at setting up a new raid 5, not adding drives to the existing array. So basically taking exchange offline, backing up the exchange db to another server, removing the existing array, building a new one, then restoring the db to the new array. My initial feeling said the data backup/restore would take siginificantly longer and the raid initialization would be fairly quick, then the dell tech layed out that number which I just didn't believe.

I'll take a look at the linked doc.
 
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