[j-nsp] Memory questions.

Magdy Albatooty (EG/EEL) magdy.albatooty at ericsson.com
Mon Jul 14 09:20:32 EDT 2003


	Regarding the tight memory space, will the system generate an early alert/alarm if there is actually low memory space available?


-----Original Message-----
From: Kevin Oberman [mailto:oberman at es.net]
Sent: Mon, July 07, 2003 8:39 PM
To: Magdy Albatooty (EG/EEL)
Cc: juniper-nsp at puck.nether.net
Subject: Re: [j-nsp] Memory questions. 

> From: "Magdy Albatooty (EG/EEL)" <magdy.albatooty at ericsson.com>
> Date: Sun, 6 Jul 2003 10:42:53 +0200 
> Sender: juniper-nsp-bounces at puck.nether.net
> Hi,
> 	The command "show system virtual-memory" displays the following:
> Memory Totals:  In Use    Free    Requests
>                          5497K     80K    15304448
> Why is free space too low? Is this normal?
> Also, command "show system storage" shows several 100% capacity. Is this normal?

Under the hood, JunOS is FreeBSD and (like several other flavors of
UNIX), it creates "special" file systems to allow access to kernel
stuff like devices and the like. These (/dev and /proc) are always at
100%, by definition.

JunOS also uses FreeBSD "vn" (vnode) devices to mount several odds and
ends. These are actually complete file systems written to a single
disk file. While they may be created as read-write file systems and
have free space, in the case of JunOS they are read-only and the file
systems are created exactly big enough to hold the desired information,
so they are always at 100%.

"ad" devices are "real" disk partitions. "mfs" is also "real", but it
exists in memory (Memory File System) rather than on a physical

As to the memory situation, what you are seeing is not unusual for
FreeBSD. It typically keeps a lot of memory that is "free" in the used
category so that it can be paged back in if needed. If memory is
needed, it is available, but if it needs to be paged in, it's already

I will admit that 80K does look a bit tight, but it is probably not.
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net			Phone: +1 510 486-8634

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