hardware raid v. dynamic disks

[galloshes]

I have a Compaq ML370 which I am installing in preparation for an Oracle 9ias setup.

I have setup the 4 9gb drives as a single raid 5 array using the Compaq drive config utility and using disk mangement have configured 3 lettered drives (C: Os D: oracle 9ias E: forms) with 36mb eisa compaq partition. I have also converted the drives to dynamic disks.

Given that I have proper hardware raid and all the performance and redundancy benefits this brings- is there any advantage to be gained by running dynamic disks?

thanks
Galloshes

 

[ReddLefty]

The only real advantage of using dynamic disks is to support software disk utilities such as Mirroring. If it's done via hardware (like in your case) then leave them as basic disks...

Another reason I don't use them is that my Ghost version (7.0) doesn't support dynamic disks. I'm not sure about v7.5, someone would need to confirm it.





"In space, nobody can hear you click..."

 

[EntilzaSte]

Dynamic disks allow you to change the "partition" size without losing data. So if you add another disk into your array you can "expand" into that disk without having any problems....

 

[AlexIT]

EntilzaSte is incorrect, if you have a hardware RAID 5 set and you want to add another disk you must re-create the entire volume, dynamic disk will only support changing the size of the existing volume.

 

[EntilzaSte]

AlexIt, wont the array automatically handle the inclusion of another disk? We have recently added a 9th disk to our array and we got the increased size for data storage without recreating the array.

Surely by having dynamic disks (something I have only used in a nonraid setup) it would allow growth?

Apologies if I have mislead anyone, but I myself am now somewhat bemused....

 

[NortonES2]

With RAID 5 you can increase the size of the array (at least with HP \Compaq servers you can) though you can't increase the partition siz. I guess this is where dynamic disks come into play otherwise you would need to purchase 3rd party software to do this.

-------------------------------

If it doesn't leak oil it must be empty!!

 

[AlexIT]

A hardware RAID 5, consists of minimum three disk array with ~30% of the combined total being used for the mirrored file table. The remaining space used as both stripe and mirror (all data is on minimum of two disks, but stored to whichever two disks had fastest write-response time at moment of save.)

If you add a drive to the RAID 5 array, you must re-build the volume because it must re-create the file table on all the drives.

If you have a failure, since everything is on two drives at the same time, you just replace with another drive that is identical to the rest, and the RAID 5 will be able to re-write everything that should be on that drive. This is why you use a RAID 5 array (faster writes than RAID 1 - mirroring, more safety than RAID 0 - striping.)

 

[AtlantaTerry]

A year ago (about August 2002) I got an email from 3Ware about this very issue.

A client wanted me to build a RAID system with a minimum of drives then add more as his capacity needs grew.

At the time 3Ware's controller wouldn't do a dynamic rebuild of the RAID if one or more new drives were added. But, the engineer said, they were re-writing the ROM code to add this capability.

Since the client didn't have the $25K (US) budget I never built the system so have no idea what the current capability of 3Ware's RAID hosts can do.

I do know, however, that they 3Ware has 32bit and 64 bit RAID hosts which use Serial ATA hard drives. So the cable installation would be much cleaner. Plus SATA supports hot swapping, unlike the old parallel ATA spec. If I were to now quote and build a 2 Terabyte box like this client wanted a year ago, I'd certainly use a Supermicro motherboard with 64 bit PCI slots and a 64 bit 3Ware RAID host which supported 12 hard drives. Then I'd stick a dozen 200Gb SATA drives on it = 2.4Tb. Neat!

Terry Thomas
PC Tech Support
Atlanta, Georgia USA