Quoting Bob Friesenhahn <bfrie...@simple.dallas.tx.us>:
What function is the system performing when it is so busy?
The work load of the server is SMTP mail server, with associated spam and virus scanning, and serving maildir email via POP3 and IMAP.
Wrong conclusion. I am not sure what the percentages are percentages of (total RAM?), but 603MB is a very small ARC. FreeBSD pre-assigns kernel memory for zfs so it is not dynamically shared with the kernel as it is with Solaris.
This is the min, max, and actual size of the ARC. ZFS is free to use up to the MAX (2098.08M) if it decides it wants to. Depending on the work load on this server it will go up to 2098M (as in Ive seen it get to that size on this and other servers), just with its usual daily work load it decides to set this to around 600M. I assume it decides it's not worth using any more RAM.
The ARC is "adaptive" so you should not assume that its objective is to try to absorb your hard drive. It should not want to cache data which is rarely accessed. Regardless, your ARC size may actually be constrained by default FreeBSD kernel tunings.
I guess then that ZFS is weighing up how useful it is to use more than 600M and deciding that it isnt that useful....? Anyway, Ive just forced the Min to 1900M so will see how this goes today.
The type of drives you are using have very poor seek performance. Higher RPM drives would surely help. Stuffing lots more memory in your system and adjusting the kernel so that zfs can use a lot more of it is likely to help dramatically. Zfs loves memory.
thanks Bob, and also to Matt for your comments... _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
