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Write back cache with no battery for replaceable data?

G

gerbiaNem

2[H]4U
Joined
Mar 6, 2005
Messages
2,169
I'm wondering if I need to spend the extra money on a backup battery unit for a media raid 5. It's going to be mainly movies and music that I can replace if need be. And I can copy files over to it then delete them from the source later. My raid card writes to the hard drive every 4 seconds from cache when inactive.

Would it be smarter to just use write through? I'll mostly be reading from the array (7x 1TB drives, 1 for parity, so 6tb total).

Also.. I'm writing and the power goes down, is there a chance of corrupting the entire raid 5 array?
 
Yes. An array that large? With what is invested thus far, i think you should purchase a battery backup. Also, at that size, RAID 6 comes into a bit more favor, from what ive heard, not implemented.
 
I bought it just to be sure I covered most of the lose-ends. It is better to have it then to don't. I sleep better at night.
I'm finishing a 8x1TB Raid5 array.
I thing going for Raid6 is generally advised for 10+ drives
Although if you can give up more space for added security, go for it.
 
Oh, and one more advice.
Test your drives HARD in all possible scenarios, initializing the arrays etc, and do extended drive tests with programs like WDdiag or Seatools.
This could weed out a weak drive.
One of mine failed during my playtime with this setup and I'm RMAing it as I type this.
Thank god my data was not on it yet, or I would see how rebuild looks like way to soon for my taste :)
 
I see the logic to just having the spare battery as a safeguard. I just don't like the idea of having to replace it every year or two (i'm weird that way). As far as raid 6, I can keep the whole array down if one drive goes so that there's little risk of another failing. So extra redundancy isn't really a problem. And ya, I will test the drives out to the max. Thanks for the advice!
 
I don't think you really MUST replace it that often.
Unless you are really anal that way.
You have a built in test in the controller that can check your capacity.
I would replace it when it is very low, and even then I wouldn't treat is as an emergency.
 
True, even if it degrades to 40%, that's still enough time to keep it running for a few seconds to write the data to the array.
 
XS Janus said:
I thing going for Raid6 is generally advised for 10+ drives
Although if you can give up more space for added security, go for it.
Click to expand...

Really, more than single digits in a single array isn't recommended. Past that one should go for multiple smaller arrays concatenated or striped together.
 
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