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On 16/06/2020 12:26, Dale wrote: |
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> I've also read about the resilvering problems too. I think LVM |
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> snapshots and something about BTFS(sp?) has problems. I've also read |
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> that on windoze, it can cause a system to freeze while it is trying to |
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> rewrite the moved data too. It gets so slow, it actually makes the OS |
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> not respond. I suspect it could happen on Linux to if the conditions |
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> are right. |
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> |
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Being all technical, what seems to be happening is ... |
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Random writes fillup the PMR cache. The drive starts flushing the cache, |
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but unfortunately you need a doubly linked list or something - you need |
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to be able to find the physical block from the logical address (for |
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reading) and to find the logical block from the physical address (for |
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cache-flushing). So once the cache fills, the drive needs "down time" to |
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move stuff around, and it stops responding to the bus. There are reports |
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of disk stalls of 10 minutes or more - bear in mind desktop drives are |
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classed as unsuitable for raid because they stall for *up* *to* *two* |
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minutes ... |
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> I guess this is about saving money for the drive makers. The part that |
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> seems to really get under peoples skin tho, them putting those drives |
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> out there without telling people that they made changes that affect |
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> performance. It's bad enough for people who use them where they work |
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> well but the people that use RAID and such, it seems to bring them to |
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> their knees at times. I can't count the number of times I've read that |
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> people support a class action lawsuit over shipping SMR without telling |
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> anyone. It could happen and I'm not sure it shouldn't. People using |
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> RAID and such, especially in some systems, they need performance not |
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> drives that beat themselves to death. |
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Most manufacturers haven't been open, but at least - apart from WD - |
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they haven't been stupid either. Bear in mind WD actively market their |
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Red drives as suitable for NAS or Raid, putting SMR in there was |
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absolutely dumb. Certainly in the UK, as soon as news starts getting |
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round, they'll probably find themselves (or rather their retailers will |
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get shafted with) loads of returns as "unfit for purpose". And, |
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basically, they have a legal liability with no leg to stand on because |
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if a product doesn't do what it's advertised for, then the customer is |
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*entitled* to a refund. |
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Dunno why, I've never been a WD fan, so I dodged that bullet. I just |
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caught another one, because I regularly advise people they shouldn't be |
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running Barracudas, while running two myself ... :-) |
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Cheers, |
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Wol |
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