chronos's questions

I have RAID1 md0 for /boot consisting of 4 partitions (sda2, sdb2, sdc2, sdd2). I'm using GPT on 2TB HDDs, so first partitions on each disk (sda1, ...) are 1-megabyte bios_grub partitions.

I also have RAID10 md1 for LVM (containing /) and RAID0 md2 for swap, both built from partitions on all 4 drives.

mdadm persistant superblock version is 0.9.

Grub was installed with something like grub-install --modules="mdraid lvm" '(hd0)' on all 4 drives (hd0, hd1, hd2, hd3).

The problem.

On reboot, grub2 fails with "error: no such disk" and displays "grub rescue>" prompt. ls command only shows 4 disks and their partitions - but no md* devices. Trying insmod normal again gives "error: no such disk.". Examining 'root' and 'prefix' shows something like '(md0)/grub', which is correct. Doing set prefix=(hd0,2)/grub and then insmod normal allows to boot normally.

The question.

Why grub2 doesn't see md0?

So far the only solution I can see is to manually build grub image with hard-coded working prefix (grub-mkimage --prefix='(hd0,2)/grub'), then use grub-setup to write the image to each disk. However, this solution is ugly, and error-prone (to avoid errors, will need to investigate how grub-install calls these two commands). I will appreciate better solutions. (Note: this is a remote server, so cannot really do 'reboot debugging'.)

I have Ubuntu server with 1x2TB HDD and 1x128GB SSD (unused). There are 2 partitions: /boot, and a physical volume for LVM, which has 1 group and 5 logical volumes: /, /var/log, /home, /srv, /tmp.

Recently the 2nd 2TB HDD arrived. We need better redundancy, so I'm looking at either joining 2 HDDs into 1 RAID1 (with /boot, /, and an LVM partition with /home, /var/log, /srv, /tmp), or adding 2nd HDD as LVM physical volume, and using LVM mirroring for logical partitions.

In addition to redundancy, I need to achieve 2 more goals: - relatively safe change from 1xHDD to 2xHDDs (I'm administering remotely a live system) - easy future extensions of LVM partitions.

Here, is RAID1 superior to LVM mirroring? (I believe it is. I'm talking software RAID1 here.)

If it is - what would be the best way to convert a 1xHDD live system to a 1xRAID1 live system remotely, if all I have is an empty 128GB SSD, and all HDD data currently fits onto it easily?

I have configured my server's sshd to listen on a non-standard port 42.

However, at work I am behind a firewall/proxy, which only allow outgoing connections to ports 21, 22, 80 and 443. Consequently, I cannot ssh to my server from work, which is bad. I do not want to return sshd to port 22.

The idea is this: on my server, locally forward port 22 to port 42 if source IP is matching the external IP of my work's network. For clarity, let us assume that my server's IP is 169.1.1.1 (on eth1), and my work external IP is 169.250.250.250. For all IPs different from 169.250.250.250, my server should respond with an expected 'connection refused', as it does for a non-listening port.

I'm very new to iptables. I have briefly looked through the long iptables manual and these related / relevant questions:

• iptables question: forwarding port x to an ssh port of different machine on the network
• How can I port forward with iptables?

However, those questions deal with more complicated several-host scenarios, and it is not clear to me which tables and chains I should use for local port-forwarding, and if I should have 2 rules (for "question" and "answer" packets), or only 1 rule for "question" packets.

So far I have only enabled forwarding via sysctl. I will start testing solutions tomorrow, and will appreciate pointers or maybe case-specific examples for implementing my simple scenario.

Is the draft solution below correct?

iptables -A INPUT [-m state] [-i eth1] --source 169.250.250.250 -p tcp
    --destination 169.1.1.1:42 --dport 22 --state NEW,ESTABLISHED,RELATED
    -j ACCEPT

Should I use the mangle table instead of filter? And/or FORWARD chain instead of INPUT?