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Symm_Unlimited
1 Copper

Actual thin device size, which it occupies in cache, when used in Virtual Provisioning

When we create a thin device, we specify its size in cylinders for example:"create dev count=2, size=1150 cylinders, emulation=FBA, config=TDEV;".

We all know that the thin device actually does not occupy any storage space. It occupies some space in the cache.

What is the actual thin device size, when it is first created?

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2 Replies
Neel_c
2 Bronze

Re: Actual thin device size, which it occupies in cache, when used in Virtual Provisioning

I don't think tdevs actually have any size. However when they are bound to a pool they get extents allocated to them from the pool. Possible 768kb for each tdevs or meta members(in case your tdev is a meta)
I am not sure on this though..would appreciate if anyone else can confirm it

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haralson
2 Bronze

Re: Actual thin device size, which it occupies in cache, when used in Virtual Provisioning

Hi,

When a TDEV is created, it occupies space in Symmetrix cache (metadata) and space in the VP pool (disk).

Depending on the type of allocation request, this could be different.  Assuming no explicit allocation request, each TDEV get's an allocation of 1 extent in VMAX platforms which is 768kb in size.  For a Symmetrix metavolume, each member will get a single allocated extent.

For cache, each TDEV takes an initial ~140kb of space, along with 8kb of additional space per usable GB.