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:
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?
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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