60 lines
2.7 KiB
Markdown
60 lines
2.7 KiB
Markdown
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---
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date: 2017-05-03
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title: Extend cached Logical Volume
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category: linux
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---
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You cannot do this directly for reasons that I have not tried to understand, but I suspect "it is hard" may have something to do with it.
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The process is:
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1. Mark your cached LV as `uncached`
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2. Extended your LV
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3. Recreate your cache
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Simple, except there are some gotchas. The process of uncaching your LV will delete your cache volumes, so you may need to find out how you previously created them. I used:
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```
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[root@localhost ~]# lvs -a -o +devices
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LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert Devices
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root cl -wi-ao---- 7.09g /dev/vda2(231)
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swap cl -wi-ao---- 924.00m /dev/vda2(0)
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[cache] data Cwi---C--- 512.00m 0.61 0.75 0.00 cache_cdata(0)
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[cache_cdata] data Cwi-ao---- 512.00m /dev/vdc(1)
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[cache_cmeta] data ewi-ao---- 12.00m /dev/vdc(129)
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lv data Cwi-aoC--- 5.00g [cache] [lv_corig] 0.61 0.75 0.00 lv_corig(0)
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[lv_corig] data owi-aoC--- 5.00g /dev/vdb(0)
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[lv_corig] data owi-aoC--- 5.00g /dev/vdc(0)
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[lvol0_pmspare] data ewi------- 12.00m /dev/vdc(132)
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```
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Here you can see:
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* that my cached LV is `lv`
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* it uses `cache` for its pool
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* The LV `[cache]` has 2 other lines associated with it:
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* `[cache_cdata]` and `[cache_cmeta]`
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* Both on `/dev/vdc`
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* 512MB and 12MB respectively
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* In the `Devices` column, `lv` that is on `lv_corig`
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* itself on `/dev/vdb` and `/dev/vdc`
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From all that we know our basic volume data is stored on `/dev/vdb` and cached on `/dev/vdc`. Naturally this means that our new device will `/dev/vdd`, although check first with `lsblk`.
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```
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pvcreate /dev/vdd
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vgexend data /dev/vdd
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# remove the cache and extend the volume
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lvconvert --uncache data/lv
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lvextend -L +1G data/lv /dev/vdd
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# Recreate the cache using the data you collected above
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lvcreate -L 512M -n cache data /dev/vdc
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lvcreate -L 12M -n cache_meta data /dev/vdc
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lvconvert --type cache-pool --cachemode writethrough --poolmetadata data/cache_meta data/cache
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lvconvert --type cache --cachepool data/cache data/lv
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```
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Now you can resize the file system if necessary, but that is left as a (not very difficult) exercise for the reader.
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