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On Tue, May 19, 2015 at 11:22 AM, <gottlieb@×××.edu> wrote: |
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> On Tue, May 19 2015, Peter Humphrey wrote: |
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> |
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>> On Tuesday 19 May 2015 10:53:26 Rich Freeman wrote: |
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>>> On Tue, May 19, 2015 at 10:44 AM, Peter Humphrey <peter@××××××××××××.uk> |
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>> wrote: |
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>>> > Incidentally, what's the received wisdom on frequency of file-system |
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>>> > trimming on SSDs these days? I've seen values quoted between twice a day |
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>>> > and once a week. And how does trimming affect btrfs? |
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> |
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> I included "discard" in fstab for my ssd filesystems, presumably |
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> following some installation guide. For example I have |
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> |
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> /dev/sda5 / ext4 noatime,discard 0 1 |
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> /dev/vg/local /local ext4 noatime,discard 0 2 |
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> |
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> Is it preferred to instead issue explicit trim's via cron? |
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> |
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It depends. |
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In theory giving your drive useful information about allocation now is |
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better than giving it the information later. The drive can make use |
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of that information to improve performance. |
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In practice some drives have brain-dead firmware and they'll do stupid |
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things with that information. If you trim part of an erase block, the |
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drive should just file that info away and make use of that information |
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when it can. However, some drives will immediately copy/erase the |
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rest of the block at that moment, which creates an unnecessary erase |
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cycle and creates IO load at a moment that the drive is already busy. |
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So, if your drive isn't brain-dead discard is better. If your drive |
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is brain-dead fstrim is almost as good if the drive isn't too full. |
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I've yet to test discard and see how well it works. |
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-- |
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Rich |
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