Tracing Disk Activity
Charles Swiger
cswiger at mac.com
Mon Nov 22 09:12:56 PST 2004
On Nov 21, 2004, at 2:17 PM, Hanspeter Roth wrote:
> On Nov 21 at 10:50, Chuck Swiger spoke:
>> Hanspeter Roth wrote:
>>> I have set an idle timeout for the hard-disk. But when there is no
>>> user activity there are frequent disk accesses.
>>
>> Yes, this is Unix. Even when there is no user activity, a Unix system
>> normally is still running a number of daemons such as syslogd which
>> regularly write to the filesystem. Beyond that, the syncer mechanism
>> tries
>> to reduce the number of dirty memory buffers every thirty seconds or
>> so.
>
> I guess that some daemons are causing disk access. But it must be
> not only syslogd.
That's right. Normally, people end up running a number of daemons like
sendmail or some other MTA, ntpd, named, etc.
> Is the syncer causing the disk to spin up even if there is nothing to
> flush?
Probably no. However, if you have active processes running on the
system, it is very likely that the syncer will find data that it does
want to write.
> [...]
>> Instead you probably will need to mount filesystems read-only and
>> create
>> RAM disks in a fashion similar to booting off limited-write media like
>
> My idea is to transfer those files that are written also when the
> user is idle to a RAM disk (some from /var/log and dhclient.leases).
> But I don't want to mount the filesystems read-only.
OK. However, you are probably not going to be able to prevent
everything running on a normal Unix system that wants to scribble to
disk short of heroic measures.
>> Compact Flash. Either that, or simply shutdown the system or run zzz
>> to
>> suspend the system via APM/APCI.
>
> This is less convenient and probably doesn't work on my laptop. (I
> have to check whether the upgrade to 5.3R has changed something in
> this respect.)
Hmm. For what it is worth, it's taken about two years of effort by
Apple to work through many of these issues in order to get MacOS X on
their laptops to be reasonably friendly in terms of saving power,
conserving hard drive access, and having power save/suspend to RAM
behave properly.
--
-Chuck
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