Computergeekery trivial shennanigans

Raid 5 to 6 conversion possible?

A recent post on Raj’s blog made me think about giving RAID6 a play. This then makes me wonder whether a RAID 5 to 6 conversion is possible? I guess this is completely impossible without a complete reformatting. But there again growing a RAID 5 array is also a similar experience, and this is now possible. I would suggest that both require adjustment of stripes. or am I really talking out of my behind?

I recently used mdadm’s new grow function to increase my 3 drive RAID5 array to 4 drives. This worked perfectly. I trust my backups, so am quite happy to risk its integrity to convert to RAID6. Hmmmm!


MythTV Unifies Personal Video Recording And Home Theatre Technology | Tom’s Hardware UK and Ireland

MythTV Unifies Personal Video Recording And Home Theatre Technology | Tom’s Hardware UK and Ireland

Great review of MythTV. Well actually a a comparison agaisnt the Windows Media Centre, but well in favour of MythTV.

My box has been running for a few months now as the only TV/DVD box I use. Pre


Growing a RAID5 array – MDADM

With the release of kernel 2.6.17, there’s new functionality to add a device (partition) to a RAID 5 array and make this new device part of the actual array rather than a spare.

I cam across this post a while ago on the LK list.

LKML: Sander: RAID5 grow success (was: Re: 2.6.16-rc6-mm2)

So I gave it a go. My HOME directory is mounted on a 3x70gb SCSI RAID5 array. so I tried adding a further drive.

Although with the release of mdadm > 2.4 the only real critical part of the process is safer (it backs up some live data that is being copied), I didn;t fancy risking growing a mounted array. So I did plenty of backups, then switched to single user run level.

Basically the step includes adding a disc to the array as a spare, then growing the array onto this device.

mdadm --add /dev/md1 /dev/sdf1
mdadm --grow /dev/md1 --raid-devices=4

This then took about 3 hours to reshape the array.

The filesystem the needs to be expanded to fill up the new space.

fsck.ext3 /dev/md1
resize2fs /dev/md1

I then remounted the drive and wahey. Lots extra space….! Cool or what

EDIT  It’s over 18 months since I wrote this post, and Linux kernel RAID and mdadm have continued to move on. All the info here is still current, but as extra info check out the Linux RAID Wiki.

EDIT 2  The Linux Raid Wiki has moved


mdadm: what a cool utility.

mdadm is really a cool utility. I decided to move my 6 drive RAID 5 array from my normal workstation to a fileserver stuck somewhere in the attic. prompted in no small part by excess heat and noise in my little office. The fileserver is an old dual Xeon pIII running Debian Sarge that should suffice.

Anyway I umounted the array, stopped it and turned it off. Plugged it into the new server. Booted it. I then just ran:

mdadm --assemble /dev/md1 /dev/sd[cdefgh]and off it goes!! Since the array was never degraded, it doesn’t even need to be resynced.

I then mounted it as usual and Bob is most deffo your uncle!

This is the first time I have installed Debian for 3 years. I am pretty impressed by the new Debian Installer. More or less 1 hour from burning the CD to booting the machine. Nice!

Computergeekery trivial shennanigans

Software vs Hardware Raid in Linux

Software vs Hardware Raid in Linux

An interesting real case experiment of various raid levels, and file system options.

Using RAID 5 with chunk of 128k, and Ext3 with a stride of 16 and block of 4k seems to be the best!
..and something that suprises me is that raid 50 was slower and less cost effective in terms of available storage than Raid 5.

I spent last night reformatting my raid array into RAID 10, then kernel RAID 10 level (rather than a RAID 0 array of RAID 1 arrays), then RAID 50, before going back to RAID 5. There was no real difference in output, and since RAID 5 maximises the storage space, it was an easy decision.

Which indicates that I need a much faster external SCSI box. All the discs are 10k u160 or better. The box is only a SUN UW Box. e.g. u40. I guess the bus is completely saturated!

For anybody who wants to experminent with software RAID in linux, MDADM is really the way to go. It’s just so easy….!

mdadm -v --create /dev/md0 --raid-devices=6 --level=raid5 /dev/sd[abcdef]1

mkfs.ext3 /dev/md0

mount /dev/mdo /mnt/raid

will create, build a filesystem and mount a 6 drive RAID 5 array. I should mention that between steps 1 and 2, you really should wait until the array has finished synchronising and reconstructing itself. Although this point is not essential, it will slow things down. Also MDADM is quite clever, and leaves a drive out as a spare. It constructs the array in degraded mode. That is the array is missing a drive. This speeds things up as there are less drives to saturate the bus.

Computergeekery – Zalman HD160 Home Theatre PC Enclosures – Zalman HD160 Home Theatre PC Enclosures

Well I think I really need to build a proper HTPC from scratch (MythTV). My cobbled together box is not really a success. It’s far too noisy and slow. It’s a dual pIII 533 Xeon, with a single TV card.

This case looks to be the business. It is a similar size and shape to my Yamaha AV amp. Brushed aluminium too!

Computergeekery trivial shennanigans

It’s L-i-n-u-x, that is an Operating System – News – CentOS in the News – It’s L-i-n-u-x, that is an Operating System

This has now been everywhere, but it is truly one of the funniest things I have read for a while.

As a poor support person my admiration is unbounded by the patience this guy shows!!

trivial shennanigans

A Look at GNOME 2.14

A Look at GNOME 2.14

As you may know I really like Gnome. It’s a dammed fine Desktop. with beagle (almost realtime filesystem search n indexing!), and other cool stuff, it’s way in front of any desktop. Well apart from OSX of course!!

Computergeekery Tips

useful SED line

I wanted to comment out a few lines in a config file. This was a result of getting to single user mode on a Tru64 box, because some SCSI drives had gone missing!

Anyway Sed to to the rescue! How do I look for a string then comment out that entire line? Not beign that familar with SED I struggled but:

sed 's/.*sda6.*/#&/g' test

Works nicely!!

The “&” means the entire match, so “#&” means comment out that line! Trying to match the entire line did confuse me, as trying to use a wildcard gave me errors. Until it dawned on me… “*” means “more than one of the previous character. so “.*” means more than one of any character i.e. wildcard!


I’ve since been told that there’s a far easier way of doing this.  e.g. using the “find” function then an upper case “I”nsert, which means insert at the beginning og a line, rather than at the current location in the buffer.

Computergeekery Mac

Making a backup copy of an OSX bootable DVD

Ferg’s gaff – easy peasy DVD copying

Well I knew DD was useful on Linux for backing up DVDs withotu any bother! Well waddayaknow it works fine for OSX bootable DVDs too!!!

Cool or what!!

dd if=/dev/dvd of=DVD.iso

growisofs -dvd-compat -Z /dev/dvd=./DVD.iso