[linux-lvm] LVM2 : performance drop even after deleting the snapshot

[Roberto Fastec]

TIP and HINT
forget SSDs with LVM unless of enterprise level 
especially if you are going to use/implement the thin provisioning

How to identify an SSD of enterprise level: 
it costs from 1,00 euro per gigabyte up to 1,50 euro per gigabyte

Kind regards
Roberto Gini
Technical Manager @ www.RecuperoDatiRAIDFAsTec.it 



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Il giorno 14 ott 2022, 21:50, alle ore 21:50, Roger Heflin <rogerheflin at gmail.com> ha scritto:
>What is the underlying disk hardware you are running this on?
>virtual, spinning, ssd, nvme?
>
>On Thu, Oct 13, 2022 at 2:01 AM Pawan Sharma
><sharmapawan at microsoft.com> wrote:
>>
>> adding this to lvm-devel mailing list also.
>>
>> Regards,
>> Pawan
>> ________________________________
>> From: Pawan Sharma
>> Sent: Wednesday, October 12, 2022 10:42 PM
>> To: linux-lvm at redhat.com <linux-lvm at redhat.com>
>> Cc: Mitta Sai Chaithanya <mittas at microsoft.com>; Kapil Upadhayay
><kupadhayay at 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 :
>>
>> dump some data to lvm2 volume (using fio)
>> take the snapshot
>> delete the snapshot (no IOs anywhere after creating the snapshot)
>> 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
>> _______________________________________________
>> linux-lvm mailing list
>> linux-lvm at redhat.com
>> https://listman.redhat.com/mailman/listinfo/linux-lvm
>> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>
>_______________________________________________
>linux-lvm mailing list
>linux-lvm at 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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