Il 07-04-2017 15:50 L A Walsh ha scritto:
Gionatan Danti wrote:
I more concerned about lenghtly snapshot activation due to a big,
linear CoW table that must be read completely...
---
What is 'big'? Are you just worried about the IO time?
If that's the case, much will depend on your HW. Are we talking
using 8T hard disks concatenated into a single volume, or in a
RAID1, or what? W/a HW-RAID10 getting over 1GB/s isn't
difficult for a contiguous read. So how big is the CoW table
and how fragmented is it? Even w/fragments, with enough spindles
you could still, likely, get enough I/O Ops where I/O speed shouldn't
be a critical bottleneck...
For the logical volume itself, I target a 8+ TB size. However, what
worries me is *not* LV size by itself (I know that LVM can be used on
volume much bigger than that), rather the snapshot CoW table. In short,
from reading this list and from first-hand testing, big snapshots (20+
GB) require lenghtly activation, due to inefficiency in how classic
metadata (ie: non thinly-provided) are layed out/used. However, I read
that this was somewhat addressed lately. Do you have any insight?
--
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@assyoma.it - info@assyoma.it
GPG public key ID: FF5F32A8
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