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On Monday, September 19, 2011 03:01:32 AM Dale wrote: |
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> Alan McKinnon wrote: |
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> > On Mon, 19 Sep 2011 13:51:03 +0700 |
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> > |
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> > Pandu Poluan<pandu@××××××.info> wrote: |
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> >> I'm not sure if LVM by itself implement striping. Most likely not |
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> >> because LVM usually starts with 1 HD then gets additional PVs added. |
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> >> Plus there's the possibility that the second PV has a different size. |
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> >> |
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> >> I might be wrong, though, since all my experience with LVM involves |
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> >> only one drive. |
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> > |
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> > LVM does do striping according to the man page. I've never tried it, |
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> > mostly because LVM is the wrong place to do that IMHO. |
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> > |
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> > Use RAID for that instead and leave LVM to do what it's good at - |
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> > managing storage volumes |
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> |
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> What I was thinking about is this. You have two drives that is one lv. |
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> It has to be data stored on both drives at some point. Example, you |
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> have a data base that is 500Gbs. You have two drives that are 300Gbs |
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> each that are in the same lv. Well obviously 200Gbs has to be on a |
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> different drive. Isn't that striping which would would result in a |
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> speed increase? |
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I think you're using the wrong names for the different pieces. |
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The 2 300GB drives will be Physical Volumes (PV) |
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These 2 PVs are in the Volume Group (VG) |
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This VG has 1 LV for database. |
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This LV, as it's at least 500GB will have parts on both PVs (harddrives) |
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This will have increased performance when the data being read happens to be on |
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2 physically different drives. If you just extend over 2 (or more) drives, |
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this is not very likely as the first 300GB of data will still, physically, be |
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on the same drive. |
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To spread the data more equally (eg. sequential parts will be on alternating |
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drives) you have 2 options: |
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1) Merge the 2 drives in a single RAID0-device (for striping) |
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2) Tell LVM to use striping for the LV when creating it. |
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My personal preference would be option 1 as I agree with Alan that LVM should |
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stick to managing LVs and leave striping and other options to RAID- |
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devices/software. |
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> Now if it is like me and is only one drive, then that won't happen. |
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With only one drive, definitely not :) |
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-- |
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