Re: Why is the performance of my lvmthin snapshot so poor
Gionatan Danti <[email protected]>
| Newsgroups | gmane.linux.lvm.general |
|---|---|
| Message-ID | <[email protected]> |
Il 2022-06-14 15:29 Zhiyong Ye ha scritto: > The reason for this may be that when the volume creates a snapshot, > each write to an existing block will cause a COW (Copy-on-write), and > the COW is a copy of the entire data block in chunksize, for example, > when the chunksize is 64k, even if only 4k of data is written, the > entire 64k data block will be copied. I'm not sure if I understand > this correctly. Yes, in your case, the added copies are lowering total available IOPs. But note how the decrease is sub-linear (from 64K to 1M you have a 16x increase in chunk size but "only" a 10x hit in IOPs): this is due to the lowered metadata overhead. A last try: if you can, please regenerate your thin volume with 64K chunks and set fio to execute 64K requests. Lets see if LVM is at least smart enough to avoid coping a to-be-completely-overwritten chunks. Regards. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: [email protected] - [email protected] GPG public key ID: FF5F32A8 _______________________________________________ linux-lvm mailing list [email protected] https://listman.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/