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boundary="===============5814515201894576682==" --===============5814515201894576682== Content-Language: en-US Content-Type: multipart/alternative; boundary="_000_PUZP153MB07512B1B646868F0F8F1D205AC259PUZP153MB0751APCP_" --_000_PUZP153MB07512B1B646868F0F8F1D205AC259PUZP153MB0751APCP_ Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable adding this to lvm-devel mailing list also. Regards, Pawan ________________________________ From: Pawan Sharma Sent: Wednesday, October 12, 2022 10:42 PM To: linux-lvm@redhat.com Cc: Mitta Sai Chaithanya ; Kapil Upadhayay Subject: LVM2 : performance drop even after deleting the snapshot Hi Everyone, We are evaluating lvm2 snapshots and doing performance testing on it. This = is what we are doing : 1. dump some data to lvm2 volume (using fio) 2. take the snapshot 3. delete the snapshot (no IOs anywhere after creating the snapshot) 4. run the fio on lvm2 volume Here as you can see, we are just creating the snapshot and immediately dele= ting it. There are no IOs to the main volume or anywhere. When we run the f= io after this (step 4) and we see around 50% drop in performance with refer= ence to the number we get in step 1. It is expected to see a performance drop if there is a snapshot because of = the COW. But here we deleted the snapshot, and it is not referring to any d= ata also. We should not see any performance drop here. Could someone please help me understand this behavior. Why are we seeing th= e performance drop in this case? It seems like we deleted the snapshot but = still it is not deleted, and we are paying the COW penalty. System Info: OS : ubuntu 18.04 Kernel : 5.4.0 # lvm version LVM version: 2.02.176(2) (2017-11-03) Library version: 1.02.145 (2017-11-03) Driver version: 4.41.0 We also tried on latest ubuntu with newer version of LVM. We got the same b= ehavior. Any help/pointers would be appreciated. Thanks in advance. Regards, Pawan --_000_PUZP153MB07512B1B646868F0F8F1D205AC259PUZP153MB0751APCP_ Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable
adding this to lvm-devel mailing list also.

Regards,
Pawan
From: Pawan Sharma
Sent: Wednesday, October 12, 2022 10:42 PM
To: linux-lvm@redhat.com <linux-lvm@redhat.com>
Cc: Mitta Sai Chaithanya <mittas@microsoft.com>; Kapil Upadhay= ay <kupadhayay@microsoft.com>
Subject: LVM2 : performance drop even after deleting the snapshot
 
Hi Everyone,


We are evaluating lvm2 snapshots and doing performance testing on it. This = is what we are doing :
  1. dump some data to lvm2 volume (using fio)
  2. ta= ke the snapshot
  3. delete the snapshot (no IOs anywhere a= fter creating the snapshot)
  4. run the fio on lvm2 volume=
Here as you can see, we are just creating the snapshot and immed= iately deleting it. There are no IOs to the main volume or anywhere. When w= e run the fio after this (step 4) and we see around 50% drop in performance= with reference to the number we get in step 1.

It is expected to see a performance drop if there is a snapshot = because of the COW. But here we deleted the snapshot, and it is not referri= ng to any data also. We should not see any performance drop here.

Could someone please help me understand this behavior. Why = are we seeing the performance drop in this case? It seems like we deleted t= he snapshot but still it is not deleted, and we are paying the COW penalty.=

System Info:

OS : ubuntu 18.04
Kernel : 5.4.0

# lvm version
  = LVM version:     2.02.176(2) (2017-11-03)
  Li= brary version: 1.02.145 (2017-11-03)
  Dr= iver version:  4.41.0

We also tried on latest ubuntu with newer version of LVM. We got= the same behavior.

Any help/pointers would be appreciated. Thanks in advance.

Regards,
Pawan
--_000_PUZP153MB07512B1B646868F0F8F1D205AC259PUZP153MB0751APCP_-- --===============5814515201894576682== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://listman.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ --===============5814515201894576682==-- From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pawan Sharma Date: Thu, 13 Oct 2022 06:53:40 +0000 Subject: LVM2 : performance drop even after deleting the snapshot In-Reply-To: References: Message-ID: List-Id: To: lvm-devel@redhat.com MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit adding this to lvm-devel mailing list also. Regards, Pawan ________________________________ From: Pawan Sharma Sent: Wednesday, October 12, 2022 10:42 PM To: linux-lvm@redhat.com Cc: Mitta Sai Chaithanya ; Kapil Upadhayay Subject: LVM2 : performance drop even after deleting the snapshot Hi Everyone, We are evaluating lvm2 snapshots and doing performance testing on it. This is what we are doing : 1. dump some data to lvm2 volume (using fio) 2. take the snapshot 3. delete the snapshot (no IOs anywhere after creating the snapshot) 4. run the fio on lvm2 volume Here as you can see, we are just creating the snapshot and immediately deleting it. There are no IOs to the main volume or anywhere. When we run the fio after this (step 4) and we see around 50% drop in performance with reference to the number we get in step 1. It is expected to see a performance drop if there is a snapshot because of the COW. But here we deleted the snapshot, and it is not referring to any data also. We should not see any performance drop here. Could someone please help me understand this behavior. Why are we seeing the performance drop in this case? It seems like we deleted the snapshot but still it is not deleted, and we are paying the COW penalty. System Info: OS : ubuntu 18.04 Kernel : 5.4.0 # lvm version LVM version: 2.02.176(2) (2017-11-03) Library version: 1.02.145 (2017-11-03) Driver version: 4.41.0 We also tried on latest ubuntu with newer version of LVM. We got the same behavior. Any help/pointers would be appreciated. Thanks in advance. Regards, Pawan -------------- next part -------------- An HTML attachment was scrubbed... URL: