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On Mon, Jul 9, 2012 at 3:12 PM, Florian Philipp <lists@×××××××××××.net> wrote: |
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> Am 09.07.2012 19:26, schrieb Jarry: |
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>> Hi, |
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>> |
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>> I'm building small server for VPS-hosting purpose (not decided |
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>> yet, probably KVM or ESXi). Althought it is "non production", |
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>> reliability is still issue for me. I'm considering using two |
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>> small SSD (ie. Intel 313, 24GB, SLC) in hw-raid1 (Adaptec 3805) |
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>> just for hypervisor, and 2xHDD/raid1 for VPS. |
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>> |
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>> I started looking for info on internet but results are not |
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>> conclusive. Opinions vary from "no problem, use SSD&raid1" |
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>> to "using SSD in raid is not recommended no matter if it is |
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>> SW or HW". Mostly missing trim-command is mentioned as reason |
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>> for not using SSD in any raid. |
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>> |
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>> Does anyone have any experience with SSD in raid (SW or HW)? |
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>> Is it safe to use it on server? |
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>> |
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>> Jarry |
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> |
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> I don't think trim is currently supported in mdaid. AFAIK dmraid |
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> supports it as long as the RAID controller plays along. I'm unsure about |
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> LVM mirrors. |
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> |
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> But trim is not your only issue: mdraid and LVM as well as most (all?) |
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> hardware RAIDs will mirror all blocks from one disk to the other when |
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> you assemble the RAID-1. This means that all blocks on your second SSD |
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> will immediately be marked dirty which incurs a significant performance |
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> penalty. |
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|
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Well, yes and no. Yes, there will be a performance penalty from having |
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all the blocks marked dirty. But this would eventually happen anyway! |
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On the other hand, once all blocks are marked dirty, you have |
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performance _stability_. If you're in a position to care about |
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predictive performance metrics, stability is quite useful. |
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|
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-- |
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:wq |
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