zfs discuss - Apr 2009 - How to set a minimum ARC size?

We have an IMAP server that uses ZFS filesystems for all of its
mailbox and database files.  As the number of users increases,
with a consequent increase in the number of processes, the ARC
size decreases from 10 gigabytes down to 2 gigabytes.  I know that
it''s supposed to do that, but in this case ZFS is starved for memory
and the whole thing slows to a crawl.  Is there a way to set a
minimum ARC size so that this doesn''t happen?

We are going to upgrade the memory, but a lower limit on ARC size
might still be a good idea.

-- 
-Gary Mills-    -Unix Support-    -U of M Academic Computing and Networking-

Gary Mills wrote:
> We have an IMAP server that uses ZFS filesystems for all of its
> mailbox and database files.  As the number of users increases,
> with a consequent increase in the number of processes, the ARC
> size decreases from 10 gigabytes down to 2 gigabytes.  I know that
> it''s supposed to do that, but in this case ZFS is starved for
memory
> and the whole thing slows to a crawl.  Is there a way to set a
> minimum ARC size so that this doesn''t happen?
>
> We are going to upgrade the memory, but a lower limit on ARC size
> might still be a good idea.
>   
This sounds like an excellent case for considering an L2ARC -- a 32GB 
(or more) extension of the ARC on an SSD.

Unfortunately, this isn''t in Solaris 10 yet.

-- 
Andrew