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From: Zdenek Kabelac <>
To: LVM general discussion and development <>,
	Erwin van Londen <>
Subject: Re: [linux-lvm] [EXTERNAL] Re: LVM2 : performance drop even after deleting the snapshot
Date: Thu, 20 Oct 2022 20:19:12 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Dne 17. 10. 22 v 15:41 Erwin van Londen napsal(a):
>  From the looks of it the disk, as provisioned out of an Azure pool, is likely 
> backed by an enterprise raid array. When you provision the pools with 
>   discard_passdown the removal of the snapshot will also be pushed down to the 
> underlying hypervisor or disk array. You would need to wait till that process 
> is completed in order to make any comparisons.
> ThinVolGrp-ThinDataLV-tpool: 0 1006632960 thin-pool 1 4878/4145152 
> 8325/7864320 - rw discard_passdown queue_if_no_space - 1024
> As per man page
> --discards passdown|nopassdown|ignore
> Specifies how the device-mapper thin pool layer in the kernel should handle 
> discards. ignore causes the thin pool to ignore discards. nopassdown causes the
> thin pool to process discards itself to allow reuse of unneeded extents in the 
> thin pool. passdown causes the thin pool to process discards itself (like
> nopassdown) and pass the discards to the underlying device.
> Try the same operation after changing the thin volume
> lvchange --discards nopassdown VG/ThinPoolLV

Discard here is likely irrelevant - since there will likely no blocks for 

When the user removes thin LV  (which happens to be sharing its block with 
some other thin LV  (origin -> snapshot)) there is just some metadata update 
reducing sharing of blocks with origin thinLV - so nothing to be discard for 
data (since snapshot is removed after its creation without any use - only if 
the origin would be meanwhile in this short period of time changed 
dramatically - then exclusively owned parts of such snapshot may be discarded)



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  reply	other threads:[~2022-10-20 18:19 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-12 17:12 [linux-lvm] LVM2 : performance drop even after deleting the snapshot Pawan Sharma
2022-10-13  6:53 ` Pawan Sharma
2022-10-13 10:50   ` Zdenek Kabelac
2022-10-14 19:31     ` [linux-lvm] [EXTERNAL] " Mitta Sai Chaithanya
2022-10-17 13:10       ` Zdenek Kabelac
2022-10-17 13:41         ` Erwin van Londen
2022-10-20 18:19           ` Zdenek Kabelac [this message]
2022-10-18  3:33         ` Pawan Sharma
2022-10-18 11:15           ` Zdenek Kabelac
2022-10-14 19:50   ` [linux-lvm] " Roger Heflin
2022-10-14 20:28     ` Roberto Fastec
2022-10-17  5:01       ` Kapil Upadhayay
2022-10-17 15:16       ` Demi Marie Obenour

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