topic Re: Migrating from Raid0 to Raid5 in Disk Enclosures

Migrating from Raid0 to Raid5

Mike Sylvan — Mon, 27 Oct 2003 10:18:39 GMT

A previous collegue of ours who has now left, was tasked to setup an external array with 14 x 72GB drives with a RAID5 configuration. But it turns out that the array was configured with RAID0 and not RAID5. Therefore, if one disk fails the whole thing fails which is not good.

Is there a way we could migrate the array from a RAID0 to RAID5 without suffering any data loss???

Re: Migrating from Raid0 to Raid5

Joshua Scott — Mon, 27 Oct 2003 10:27:35 GMT

What HW are you specifically using?

RAID 0 allows 1,008 GB of available space, whereas RAID 5 will give between 792 and 936 GB of available space. Generally, you should backup the data on the array, and then restore it once you change the configuration to RAID 5. Some configurations MAY allow you to migrate, but I doubt it.

Either way, you should definitely backup the data before trying anything.

Re: Migrating from Raid0 to Raid5

Mike Sylvan — Mon, 27 Oct 2003 10:47:36 GMT

The hardware is a Compaq Proliant ML570 with a 5300 Array Controller installed with an external array. The array has 14 x 72.8GB drives installed. When I select the "migrate" option in the ACU and go to the help option it states that there will be no data loss. Is this correct?

Re: Migrating from Raid0 to Raid5

Paul Jerrom — Mon, 27 Oct 2003 19:32:54 GMT

Howdy. This is a VMS forum, and this isn't a VMS server. However, a couple of thoughts:
1) I think if I were doing something with a near terrabyte of data I'd probably do at least one backup first, irrespective of what the help facility said. Otherwise you too might be a previous colleague who now has left!!
2) Have a think about why you are using Raid-5. Writes will be slower that using Raid-0, due to overhead of calculating parity. There are pros and cons of each level of Raid, and in fact your best solution may be a combination of different raid levels for different data types. Typically high access databases benefit from R0+1. If it is all high volume stuff and read/write performance is not as important as availability the R5 may be the way to go. But RAID is never a substitute for backups...
3) If R5 is the best for you, you increase your availability more by having more than 1 R5 set - ie two R5 sets each with 7 disks, rather than 1 with 14. Assuming your data lends itself to it, of course.

That's my tuppence worth. All the best, PJ.

Re: Migrating from Raid0 to Raid5

Paul Jerrom — Mon, 27 Oct 2003 19:44:30 GMT

Oopsie, apologies about the VMS bit, I had wandered away from the forum where I had started.
Rest applies though...

Re: Migrating from Raid0 to Raid5

Seth Parker — Tue, 28 Oct 2003 20:53:01 GMT

Compaq/HP is usually pretty conservative about things, so if they offer the choice to migrate the data, you should be able to do it. I've not done this function, but I've added a disk into an existing RAID5 array, all while the Windows 2000 server was up and running.

Your best bet will be to upgrade to the most recent/stable versions of the array drivers and controller firmware, read everything you can about the Array Config Utility and what to expect, backup the system fully, and let it run over a weekend. I imagine that it's going to take a *long* time and that data access will be slow while the conversion takes place.

Oh, as was mentioned, since the amount of available disk space is going to decrease, you'll need to make sure that all of the existing disk space hasn't been allocated. If it has, you've got a whole separate set of problems to deal with since you OS will not be happy.

Good luck!
Seth

Re: Migrating from Raid0 to Raid5

Mike Sylvan — Wed, 29 Oct 2003 07:55:26 GMT

Thanks for your input guys.

Wish me luck!!! ;-)

Re: Migrating from Raid0 to Raid5

Mike Sylvan — Thu, 30 Oct 2003 06:44:50 GMT

Can you confirm something for me?

During a migration from RAID0 to RAID5 and the server crashes, will the migration restart when the server is brought back online?