From: Pawan Sharma <sharmapawan@microsoft.com> To: "linux-lvm@redhat.com" <linux-lvm@redhat.com>, "lvm-devel@redhat.com" <lvm-devel@redhat.com> Cc: Kapil Upadhayay <kupadhayay@microsoft.com>, Mitta Sai Chaithanya <mittas@microsoft.com> Subject: Re: [linux-lvm] LVM2 : performance drop even after deleting the snapshot Date: Thu, 13 Oct 2022 06:53:40 +0000 [thread overview] Message-ID: <PUZP153MB07512B1B646868F0F8F1D205AC259@PUZP153MB0751.APCP153.PROD.OUTLOOK.COM> (raw) In-Reply-To: <PUZP153MB075126926388815B6F9E1258AC229@PUZP153MB0751.APCP153.PROD.OUTLOOK.COM> [-- Attachment #1.1: Type: text/plain, Size: 1711 bytes --] 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 Upadhayay <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. 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 [-- Attachment #1.2: Type: text/html, Size: 5620 bytes --] [-- Attachment #2: Type: text/plain, Size: 202 bytes --] _______________________________________________ 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/
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From: Pawan Sharma <sharmapawan@microsoft.com> To: lvm-devel@redhat.com Subject: LVM2 : performance drop even after deleting the snapshot Date: Thu, 13 Oct 2022 06:53:40 +0000 [thread overview] Message-ID: <PUZP153MB07512B1B646868F0F8F1D205AC259@PUZP153MB0751.APCP153.PROD.OUTLOOK.COM> (raw) In-Reply-To: <PUZP153MB075126926388815B6F9E1258AC229@PUZP153MB0751.APCP153.PROD.OUTLOOK.COM> 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 Upadhayay <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. 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: <http://listman.redhat.com/archives/lvm-devel/attachments/20221013/3a0c62f5/attachment.htm>
next prev parent reply other threads:[~2022-10-13 7:02 UTC|newest] Thread overview: 23+ 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 [this message] 2022-10-13 6:53 ` Pawan Sharma 2022-10-13 10:50 ` [linux-lvm] " Zdenek Kabelac 2022-10-13 10:50 ` Zdenek Kabelac 2022-10-14 19:31 ` [linux-lvm] [EXTERNAL] " Mitta Sai Chaithanya 2022-10-14 19:31 ` Mitta Sai Chaithanya 2022-10-17 13:10 ` [linux-lvm] " Zdenek Kabelac 2022-10-17 13:10 ` Zdenek Kabelac 2022-10-17 13:41 ` [linux-lvm] " Erwin van Londen 2022-10-20 18:19 ` Zdenek Kabelac 2022-10-18 3:33 ` Pawan Sharma 2022-10-18 3:33 ` Pawan Sharma 2022-10-18 11:15 ` [linux-lvm] " Zdenek Kabelac 2022-10-18 11:15 ` Zdenek Kabelac 2022-10-14 19:50 ` [linux-lvm] " Roger Heflin 2022-10-14 19:50 ` Roger Heflin 2022-10-14 20:28 ` Roberto Fastec 2022-10-14 20:28 ` Roberto Fastec 2022-10-17 5:01 ` Kapil Upadhayay 2022-10-17 5:01 ` Kapil Upadhayay 2022-10-17 15:16 ` Demi Marie Obenour 2022-10-17 15:16 ` Demi Marie Obenour
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