derobert's questions

We have a XP machine which runs scheduled tasks early in the morning and unfortunately has to be logged into the desktop of a certain user for that to work. Unfortunately, that user sometimes gets logged out—either from an administrator logging in (and forgetting to log back in the correct user), or from it being restarted to apply security updates, etc.

I'd like to have Nagios monitor the currently logged in user, to confirm its the right one. Nagios is running on Linux.

So far, I've looked for an SNMP variable with the current user; I've had no luck. I tried snmpbulkwalk -m all -v2c -c community machine and grep'd it for the user name, and also did a before login & after login, and checked the diff, and found nothing useful.

I checked the net command (from Samba), but I don't see anything there—though I admit its possible I missed something. The various session options seem to only display the net session (even when I use my domain admin account).

Supposedly (see, e.g., a question about it here), with NCQ enabled drives, the drive write cache is supposed to be safe, as in it doesn't lie to the OS about data being committed to the platters when it isn't. I'm trying to figure out what settings are required to make this a reality.

I'm using diskchecker.pl to confirm if all blocks surviving a pull of the power plug. The server is configured like this:

• 4x ST3500514NS running in Linux MD RAID10. Intel 3420 chipset. In AHCI mode.
• LVM running on RAID10.
• Tested filesystem is ext4 (with barrier=1,data=ordered) on a logical volume. I also tried testing directly on a logical volume (block device); that didn't help.
• Debian 6.0 (squeeze); kernel 2.6.32-5-amd64

If I turn off write-cache (hdparm -W0), then it works (at a huge performance penalty). So it seems like the upper layers are capable.

I've tried enabling FUA in libata (by passing fua=1 to the module loading, and confirming via dmesg), that did not help.

Any suggestions on how to make this work?

edit: found the reason (see my answer); any suggestions on how to get at least some of the performance back?

We're considering building an Oracle database with 12 Intel X25-M G2 160GB drives in software RAID10. It'd be running Linux. Database gets some very heavy write activity during the early morning data load, other than that it is mostly read-only (and the read load is fairly minimal).

We're currently running on 11 150GB Velociraptors (also Linux software RAID10), and are hoping the X25-M will speed up the data load.

We currently have redo on different disks than the rest of the data.

I'm wondering a few things:

1. Any experience with using X25-M drives for databases? The X25-E are unfortunately beyond our budget.
2. Would it hurt to separate redo off to some magnetic (non-SSD) drives, say 2 (raid1) or 4 (raid10) Seagate Constellations?

There appear to be (at least) two ways to add a secondary IP address to an interface on Linux. By secondary, I mean that it'll accept traffic to the IP address, and responses to connections made to that IP will use it as a source, but any traffic the box originates (e.g., an outgoing TCP connection) will not use the secondary address.

Both ways start with adding the primary address, e.g., ip addr add 172.16.8.10/24 dev lan. Then I can add the secondary address with either a netmask of /24 (matching the primary) or /32.

If I add it with a /24, it gets flagged secondary, so will not be used as the source of outgoing packets, but that leaves a risk of the two addresses being added in the wrong order by mistake. If I add it with /32, wrong order can't happen, but it doesn't get flagged as secondary, and I'm not sure what the bad effects of that may be.

So, I'm wondering, which approach is least likely to break? (If it matters, the main service on this machine is MySQL, but it also runs NFSv3. I'm adding a second machine as a warm standby, and hope to switch between them by changing which owns the secondary IP.)

I'm trying to get our new server, a X8DTN+-F's IMPI configured to talk to our authentication servers. The two choices are LDAP and RADIUS.

I'm debugging this by looking at packet captures, as it seems the IPMI stuff doesn't log anything.

I first tried LDAP, but the IMPI stuff insisted on binding as a user other than the one logging in (wtf). Once I set it up its own user, it managed to find the user (though not by searching for the attribute I wanted, and there seemed no way to change it), but even upon getting a response... didn't allow the login. Maybe it expected a password attribute in the response, which of course it didn't get. It should just bind as the user who is logging in (and should use LDAP over SSL, but that's another story).

So I tried RADIUS. Now, it sends the expected Access-Request packet (with expected username, an encrypted password, a NAS IP Address of 127.0.0.1 [wtf], and a port of 1). It then gets back an access-accept packet, with a service-type of Administrative-User… and then it rejects the login.

(Note: by rejects the login, I mean redisplays the login page. Its not like this thing believes in error messages. Or logs.)

So, is there some magic attribute I need to get the RADIUS server to reply with? Has anyone gotten RADIUS to work with Supermicro's IPMI