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Re: [linux-lvm] Thin provisioned LV + raid5?



On 01/25/2014 10:26 PM, Vasil Valchev wrote:
Hello,

I want to create a thin pool that will be used for storing virtual machines
(inside separate thin volumes).
The thing is I can't find if that thin pool can be at the same time --type
raid5 (or similar) at the same time?

Would something like this be possible:

lvcreate -T virtvg/virtpool -L 500G --type raid5

Or maybe the whole approach is wrong?
What I want to do in the end is a thin pool/volumes that are replicated in
some way - ideally raid5, if not - mirrored.

Is this implemented and supported in LVM, or is hardware raid recommended
to handle the redundancy in thin provisioned storage?

Hi Vasil, you have to first create the RAID5 volume first and then convert to pool using lvconvert.

Also if you want redundancy for data, you will likely want redundancy for metadata as well. RAID1 is recommended.

lvcreate -n meta --type raid1 -m 1 -L 256M virtvg
# ^ adjust number of legs (-m N)
# ^ you may want to adjust size of metadata volume, depends if you plan to further grow your pool in close future as metadata resize is still not fully working, but will soon. If my math is correct 256M should be enough for up to 2TB - see --poolmetadatasize.

lvcreate -n virtpool --type raid5 -i 3 -L 500G virtvg
# ^ adjust number of stripes (-i N)

lvconvert --thinpool vg/virtpool -c 64k --poolmetadata meta
# ^ adjust chunksize - if you want snapshots use smaller chunks, if you want to use only thin-provisioning use larger chunks. if both you have to compromise. Too small chunks may affect performance if you have many VMs issueing many concurrent writes.

-- Marian



Regards,
Vasil



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