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 LATEST TOPICS |  FORUMS » GENERAL DISCUSSIONS » HDD CACHE, HOW IMPORTANT IS CAPACITY?...
Subject: HDD cache, how important is capacity?
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Mr. Friendly™ Nov 09, 2017 03:09 PM Reply | Bookmark
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for instance if I were to set up a NAS with 5 or 6 drives in RAID 5 or 6, how important would 128MB or 256MB on an 8TB drive be?

Topic URL: http://forums.ncix.com/forums/topic.php?id=2762666

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Bruce_R Nov 09, 2017 04:08 PM Reply | Bookmark
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Reconsider RAID 5 with 8TB hdd. Rebuilding the array will take a day or more and during that time another failure will cause the loss of all data.

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Mr. Friendly™ Nov 09, 2017 04:25 PM Reply | Bookmark
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it's hypothetical Bruce. I prefer RAID 6.

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Bruce_R Nov 09, 2017 06:17 PM Reply | Bookmark
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As hdd capacities increase, RAID 6 is probably going to suffer from the same fate as 5 in a few years.

But that doesn't answer the original question. Sadly there doesn't seem to be any easily available data on the subject and a quick look at consumer NAS drives from three major manufacturers suggests that other design factors influence choice of cache size. I.E. they are all over the place.

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Entz Nov 10, 2017 11:42 AM Reply | Bookmark
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Yeah I have a feeling this is one of those there is no correct answer things. More cache = better benchmarks, especially if the work load fits in cache but in reality that is almost never the case. I would think it depends entirely on your work load and your controller (tiered or not etc)

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Yoinkerman Nov 13, 2017 09:25 AM Reply | Bookmark
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If you're rebuilding an array I don't think cache will be a bottleneck so bigger is better

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Hyperlight Nov 13, 2017 01:17 PM Reply | Bookmark
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Depends on what you want to do with the array. I actually find it makes little real world difference under standard operations. Large arrays like that are usually for sequential large data sets. If your doing tons of random IOPS on mechanical only array your doing something wrong. Look into a SSD cache buffer addon for that kind of workload. See above for my 8ch WD6TB Red Pro array at 66% capacity, 128MB cache per drive on LSI 9371 hardware RAID controller with BBU no SSD cache. Test was conducted using a my desktop that over 10gig fibre. It posts numbers far in excess of gigabit speeds which is what I assume most homes use. And FAR exceeds wireless speeds which I guess most people use sadly :( wired connections are rare as it is.

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