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On 26/08/2020 18:40, Grant Taylor wrote: |
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> On 8/21/20 10:15 PM, Caveman Al Toraboran wrote: |
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>> just to double check i got you right. due to flushing the buffer to |
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>> disk, this would mean that mail's throughput is limited by disk i/o? |
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> |
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> Yes. |
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> |
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> This speed limitation is viewed as a necessary limitation for the safety |
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> of email passing through the system. |
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> |
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> Nothing states that it must be a single disk (block device). It's |
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> entirely possible that a fancy MTA can rotate through many disks (block |
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> devices), using a different one for each SMTP connection. Thus in |
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> theory allowing some to operate in close lock step with each other |
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> without depending on / being blocked by any given disk (block device). |
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> |
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> Thank you for the detailed explanation Ashley. |
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Or think back to the old days - network was slow and disks were |
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relatively fast. The disk was more than capable of keeping up with the |
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network, and simple winchesters didn't lie about saving to the rotating |
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rust ... |
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> |
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> As Ashley explained, some MTAs trust the kernel. I've heard of others |
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> issuing a sync after the write. But that is up to each MTA's |
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> developers. They have all taken reasonable steps to ensure the safety |
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> of email. Some have taken more-than-reasonable steps. |
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> |
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Depends on the filesystem. "sync after write" was an EXTREMELY daft idea |
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on ext4 in the early days - that would really have killed system response. |
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Nowadays you could stick an SSD cache in front of a raid array ... |
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Cheers, |
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Wol |
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