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I built a W2K8 R2 server last weekend, and built a R5 array using Disk Management, 5x 1TB drives.

For the next 60 hours the status said 'Resynching (X%)' as it built the array. during this time i did read and write to the drive (slowly) and once the rebuild was complete speeds were quite fast. I was copying over some data from a USB hard drive overnight, and the machine crashed (looking in the error i believe it was the driver for the usb drive) and so the RAID5 went back to resynching, since the machine was not shut down properly.

The issue is, it's been about 48 hours since that started and I'm happy to say it will take roughly 60 hours again to resynch, however.. all this time in Disk Management, the status has only said 'Resynching', not 'Resynching (X%)'. The hard drive light is going nuts, and read/writes are slow again, so I'm assuming it is actually resynching.

The question is - is that a correct assumption? and why is disk management not telling me what %age it's done? Is this normal behaviour for a not-properly-shut-down r5 array?

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3 Answers 3

Yes, long rebuild times are pretty normal for RAID. Particularly software-based RAID. A hardware-based solution with battery backup on the controller will be less susceptible to software failures, and the battery backup should protect you from short outages.

I am not sure why windows isn't showing you a status, I never worried about that too much.

You may want to read this article Why RAID 5 stops working in 2009. Which seems to suggest that a volume that large is likely to fail. See (question).

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I do understand that if I were using a hardware based solution things would be more reliable, but this is a home server and cost is a major factor. It's mainly for storage, not for many read/writes. –  benpage Nov 19 '09 at 1:08
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Just logged in and the rebuild was complete. Don't know why it never told me it's percentage, but it was a correct assumption that it was doing the resync all that time, just so people know.

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@benpage - Thanks for the update. This kind of update is best done by editing the question rather than adding an answer –  tomjedrz Nov 19 '09 at 1:51
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@tomjedrz - thanks :) i actually am going to mark this as my answer in 2 days, as i answered my question myself –  benpage Nov 20 '09 at 5:01
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What are your reasons for using software RAID5?

If you're using software RAID 1 then that is acceptable but software RAID 5 is asking for trouble.

Once one disk fails there is a high likelihood that a second disk will fail as well. With a 60hr resync time there is a very high likelihood of a second disk failure happening before sync completion rendering the entire array unrecoverable. Also, apart from being slower, software RAID is more prone to corruption.

I would say that the effort of dealing with software RAID 5 is really not worth it. As you are ready to give up 25% of your hard disk for redundancy (assuming 4-disk RAID5) then why not go all the way, give up 50% of your space (hard drives are not too expensive these days) and run RAID 1.

Just my $0.02

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To add some cents, I'd say that performance can be higher in software as well, at least today - but the reliability is a real kicker - especially trying to identify WHICH drive failed without a controller lighting it up for you. And I wouldn't build a 5 disk RAID5 even with a trusted and expensive hardware controller... 5 disks or more is just asking for trouble, go RAID6 or at least have a hotspare imo ^^ On the other hand, it's inexpensive and, if the downtime and data loss is tolerable - why not? I mean, RAID isn't backup, it's an uptime thingie... –  Oskar Duveborn May 17 '10 at 7:19
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