Whether or not you want to use the "normal backup algorithm" is irrelevant,
since if you try and start that snapshot Postgresql /*will*/ see the
instance as /*needing*/ to be recovered.
Having said that... our storage team does SAN snapshots of the *single LUN*
where */all/**of the Postgres* files (regardless of mountpoint) reside on
"my" Postgresql server. When needed, the Linux guys restored the relevant
snapshot to a new server, changed the host name and IP address and Postgres
started right up, recovering just as if there had been a system crash.
On 5/12/22 04:10, Zwettler Markus (OIZ) wrote:
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I don't want to do use the normal backup algorithm where pg_start_backup +
pg_stop_backup will fix any fractured block and I am required to have all
archived logfiles, therefore.
I want to produce an atomic consistent disk snapshot.
I am not sure if freeze/unfreeze will be enough with default values (8k db
blocksize vs. 4k fs blocksize).
I am quite sure it should be safe when I also change the fs blocksize to
8k because 1 IO = 1 db block = 1 fs block than.
Any thoughts?
*Von:*Ron <ronljohnso...@gmail.com>
*Gesendet:* Donnerstag, 12. Mai 2022 01:51
*An:* pgsql-general@lists.postgresql.org
*Betreff:* [Extern] Re: consistent postgresql snapshot
On 5/11/22 10:41, Zwettler Markus (OIZ) wrote:
PostgreSQL12 running on CentOS7 + ext4.
Would it be save to do a "fsfreeze –freeze" + disk snapshot +
"fsfreeze –unfreeze" of the PGDATA filesystem to get a consistent
snapshot?
I am wondering as PostgreSQL default blocksize = 8k while ext4 default
blocksize = 4k, resulting in 2 fs blocks per db block.
If data/base and pg_xlog are on the same filesystem, then it might work.
Be sure to select pg_start_backup('something informative');beforehand, and
select pg_stop_backup();afterwards.
For example:
psql -c "select pg_start_backup('something informative');"
fsfreeze –freeze
/disk snapshot/
fsfreeze –unfreeze
psql -c "select pg_stop_backup();"
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