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Overhead for RAID 0+1 is too high ... should I use RAID-5?

Brett Cooper EXPERT RESPONSE FROM: Brett Cooper

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QUESTION POSED ON: 06 January 2005
I am in the process of migrating data from DASD to an enterprise-based SAN. This is one of several activities in a disaster recovery solution. A by-product of this is that I'll be left with lots of unused storage space from the legacy devices. I have a plan for these, but need some advice!

I plan to use two of the DASD (Sun 3310, 12 * 73 GB disks) to store replicated images of the boot disks from production machines. The idea here being that these can be used on the DR site to jumpstart a machine and have it quickly rebuild as a production machine, identical to how it was on the primary site before any disaster.

In terms of the storage devices, what is the best way to utilize the two 3310s? I have 24 disks, totaling around 1.7 TB of raw data. RAID 0+1 seems an option, but the overhead of this just seems obscene. How best can I utilize these 24 disks?

In terms of I/O performance, writing is not a primary consideration, but reading of data needs to be at a decent enough rate to not cause a bottleneck when jumpstarting clients. I also need to consider the fact that the units I have inherited are JBOD and do not have a hardware RAID controller.


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I would strongly suggest looking at a copy of Veritas Volume Manager and using the software-based RAID capabilities of the product to augment these JBODs. You have a good deal of storage available for your purpose, but I would suggest that you need to carve it up and make it highly available in case of a failure, as you have mentioned. Is performance a concern in the case of this type of a disaster? If so, how much will a mirrored versus a RAID-striped configuration provide in terms of trade-off?

I would say that a mirrored configuration would given you the best redundancy, and give you a couple of spare disks in case of a disk failure, while RAID may give you better performance, but you will lose a few disks for RAID parity space. In the end, I would probably just go with a simple mirror and call it a day, or look at the RAID 0+1 and pay the overhead of the disks. In the end you should have enough space to do what you need, which is the real goal.

Read Stephen Foskett's answer to this question.


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