How to make a single volume larger than 2TB?

Question

I've got an application that requires the data to be in a single directory and needs more that 2TB of storage. I've got a PE2650 running W2K with a PERC-4DC and two PV220S one with 14-146GB drive and the other with 14-300GB drives. I've considered building 3 RAID-5 drives and concatenating them to make one big dynamic volume. Can this be done? Will it be fault tolerent? If I loose one drive in any of the RAID-5 arrays will it corrupt the volume? Does anyone know for sure or have a different method of creating > 2TB volumes that are fault tolerent?

Dev Mgr · Answer

Theoretically it's possible, but if for whatever reason one of the raid-5's has a problem, you risk all your data. I have seen this happen where a customer had 3 raid-5's striped to make 1 large drive letter and one of the raid-5's turned out to have parity issues after a drive replacement. The only fix for this is to unbind the virtual drive (raid controller bios or management software) and rebind it. This meant the person in question had to back up in excess of 4TB of data to be restored once everything was rebuilt.

For this reason I personally don't recommend it.

Also, take into account the time needed to restore this much data. It's unlikely to happen (total data loss), but if it were to happen, can you afford the time it would take you to restore that much data. Even with the best backup software, restoring 2+TB can really run into quite a bit of time to restore (usually quite a bit more than it would take to back it up).

klewis-aetn.org · Answer

Yes, I understand your recommendation. But I don't have a choice. I've got to have all the data appear in one big folder and I have more than 2TB of data. If I could split this up several disks it would be a no brainer. But I need to find a way to make this happen. I thought for sure in this day and age there would be a simple way to do this. I appreciate your input. I think I'm going to run a few test to see how resilient this setup will be.

pcmeiners · Answer

Link to Intel paper on why  large arrays are not safe http://www.intel.com/technology/magazine/computing/RAID-6-0505.htm     DFS... http://www.microsoft.com/windows2000/techinfo/howitworks/fileandprint/dfsnew.asp Message Edited by pcmeiners on 07-29-2005 10:10 PM

klewis-aetn.org · Answer

Thanks for the links. Raid-6 does look interesting but it's not a option with Dell's PERC cards. DFS won't work for me either since the mount points end up as directories in the file system and I need the contents of the mounted file system to look as one big directory. I do understand the downside of single big volumes but there are applications in the video realm where single files may be 100MB or more and I've got thousands of them. But I did run some tests this last week.

I built a 3TB volume consisting of two 1.5TB Raid-5 arrays spanned (not striped) using W2K dynamic volumes with a global hot spare in place. I filled it with data and took a single drive offline in each virtual disk 5 times and let them rebuild and ran chkdsk to check for volume errors. Other than taking nearly 12 hours to rebild with 90% rebuild rate I did not run into any errors. So in the long run this obviously isn't a "supported" solution but it's the only solution given what I've got to work with and it appears that it is fault tolerent at least to a point.

pcmeiners · Answer

You do have a tough situation.

For the future

I like my SCSI drives but take a look at SATA , Tekram makes a series of SATA cards which have incredible performance, and support raid 6 , hot spares (Arec series)

http://www.areca.com.tw/products/html/pcix-sata.htm

At teakers.net, in Dutch, check out the benchmarks, benchmarks are in English

http://www.tweakers.net/benchdb/suite/13

Review

http://www.tweakers.net/reviews/557/12

Message Edited by pcmeiners on 08-02-2005 09:14 AM

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How to make a single volume larger than 2TB?

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