would vxvm mirroring activities take lower priority than normal write activity before it is synced up?

[IdaWong]

hi,

I have a question here, hoping someone could point out perhaps.

is a vxvm mirroring event (before it is sync-ed up) takes lower priority than a normal I/O data write?

the reason I am asking is because if during vxvm mirror setup, would it slow down normal data I/O

it would make sense to lower the priority of these writes than normal data I/O I would think.

thanks in advance.

[mikebounds · Accepted solution]

See extract from 6.0 release notes:

Veritas Volume Manager throttling of administrative I/O
 

In this release, Veritas Volume Manager (VxVM) provides throttling of
administrative I/O. During heavy I/O loads, VxVM throttles I/O that it creates to
do administrative operations. This behavior ensures that the administrative I/Os
do not affect the application I/O performance. When the application I/O load is
lighter, VxVM increases the bandwidth usage for administrative I/O operations.
VxVM automatically manages the I/O throttling for administrative tasks, based
on its perceived load on the storage. Currently, I/O throttling is supported for the
copy operations which use ATOMIC_COPY and involve one destination mirror.
The I/O throttling is transparent, and does not change the command usage or
output. The following commands are supported:
■ vxassist mirror
■ vxassist snapcreate
■ vxevac
■ vxplex att
■ vxplex cp
■ vxplex mv
■ vxprint
■ vxsnap addmir
■ vxsnap reattach
■ vxsd mv
■ vxtune
The administrative I/O operations allocate memory for I/O from a separate memory
pool. You can tune the maximum size of this pool with the tunable parameter,
vol_max_adminio_poolsz .
See the Veritas Storage Foundation Tuning Guide for information about tuning
the vol_max_adminio_poolsz parameter.

Mike