kbyrd's questions

I'm automating some interaction with Cisco ASA devices. I need to do the following:

1. login over ssh
2. send 'enable', provide enable password
3. send 'configure terminal'
4. send some other commands, never going to deeper level of config.
5. send exit (gets me back to enable mode prompt)
6. disable (should get me back to the basic prompt)

Then a bit later, another scripted bit tries to send 'enable' again. This time, the device asks for a username and password. Not just the enable password. This happens consistently on some devices I have tried and never on others. I'm guessing it is something to do with 'disable'. I don't have to use that command, I just need to drop from enable mode back to a regular prompt so that future bits can always expect to start from the base '>' prompt.

Apologies in advance if this is too basic of a question. Any ideas?

Using Linux mdadm, I've setup a six disk raid10,f2 array. I'm using 7200RPM SATA drives. The biggest load I am worried about is recording four streams of live video (worst case of 20Mbits each, final file size ends up being 10GB in the worst case), while watching another previously-saved file (similar characteristics).

I've been seeing glitches in the recordings that appear to be dropped frames. I suspect my the RAID array isn't keeping up, but I'd like to know more about what specifically is going on. Is it seeking too much? Is there some random wait? Is there a specific device in the array that's taking longer than the others, etc.

What sort of tools should I be using, what information should I be gathering, and how do I interpret it? Ideally, I'd like to have something gather data for several days then I could go back and look at it, but if that's not possible more live-snapshot type tools will work too.

Let's say I've got six identical drives and I'm going to use them all in a RAID10,f2 array constructed using mdadm. I've always put a single partition on each disk and constructed the array from /dev/sd[bcdefg]1 rather than the whole disk. But, I'm wondering if that's the best thing to do with a modern kernel and mdadm.

I would like to be able snapshot the system volume, mount that shadow copy, then run my own hand-rolled copy on it all from a batch file. How can I do this on Windows 7?

I am looking for a "application tunneling" solution that behaves a similar to an ssl or ssh tunnel but over UDP. One the client end, OpenVPN provides an network interface. I want the client end to just listen on a local port and forward all that traffic over the tunnel it has established.

NOTE: I used the term application tunneling to describe how ssh tunneling behaves vs. how OpenVPN behaves. With an ssh tunnel, a network application connects to localhost:12345. With OpenVPN, an network application talks to the remote IP, which is reached over a tun interface. OpenVPN requires support in the kernel for tun/tap interface, the application tunnel model does not. If someone knows the correct term for this, please let me know in the comments.

Quick and dirty summary: I want something like a write cache that drains only when the system isn't busy.

I want something along the lines of this question RAM disk and physical RAID with a slight twist.

For a particular build I'm doing often, I would like to keep build output in a ramdisk that eventually gets written out to disk. One particular target I'm building is really a bunch of cp, tar, gzip and such so I'm disk bound. In a tight debug cycle I want it to be fast, and don't care so much if the build output is destroyed by power-off. However, it would be nice if the ramdisk was synced out to disk when the system wasn't busy. I can imagine doing this with a a cron job, but I'm asking you all on the off chance there's a more coherent solution that combines the characteristics of the other question (ramdisk that overflows to disk) with this new twist (given enough idle disk time, the contents of the ramdisk make it out to disk too). Idealy, the whole thing looks like a single mountpoint, where I set the total size and the amount of ram to use.

--- updated ---

I don't think the page cache does what I want because I really want pretty fast write performance.

It seems that CPU increases have outpaced disk speed for a while. Assuming a desktop or laptop with modern dual core Intel/AMD CPU and a single average SATA disk, would doing compression on most all of the disk give better overall performance? Basically does the reduced disk bandwidth more than make up for the increased CPU load? I'm sure the real answer is "it depends on what you're doing". By asking this question, I'm hoping to have someone who has done this pipe up and give some examples or pitfalls.

I would like to mount an ext2/3 filesystem on a mac running 10.5.

I currently use rsync with --link-dest to get an incremental Time Machine-ish backup of few sources with a variety of operating systems to a single Linux box. I swap out the backup drive to an external site every so often. One of these sources is a mac and while rsyncing from the Linux box to the mac appears to work, it believe it isn't catching all the details of the HFS+ filesystem so I couldn't really do a full restore from an OS DVD if I need to. Also, it takes an awful long time to backup the mac compared to other sources with similar amounts of data and number of files. So, I thought I would use Time Machine for the macs and continue using rsync for the other sources. Is Time Machine the best way to do this? If so, what do I need to do on my Linux server to have it be a valid Time Machine target? If not, what do you suggest?

I know there are several (Time Machine to Linux) pages on the Net, but I thought ServerFault could use one.

In any of the RAID levels that use striping, increasing the number of physical disks usually increases performance, but also increase the chance of any one disk in the set failing. I have this idea that I shouldn't use more than about 6-8 disks in a given RAID set but that's more just passed down knowledge and not hard fact from experience. Can anyone give me good rules with reasons behind them for the max number of disks in a set?