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Thursday, October 11, 2007

Resurrecting old hardware...

Hardware is getting faster and faster, so people upgrade as the needs get bigger and bigger. What about the old hardware that stays behind? Some of it gets reused for low priority servers but most of them get thrown away as obsolete. The worst case is if the hardware itself has become obsolete aka its maxed out when it was current.

Well I happened to be involved in one of this type of resurrections. The server was an IBM xSeries 220 tower with 72GB hardware raid 1 array and a small 40GB IDE drive. The idea was to upgrade the small IDE to a 160GB drive to get more storage area. As the 220 has show insane stability the idea was well at the beginning, well until the new drive was installed and well, the Linux recognized it. But here is where the problems started. The performance was insane - the drive would max out at 500KB/s with the read timings test (hdparm -t /dev/hda). The other symptom was drive seek errors which would indicate that there were bad blocks at the beginning or supernodes which would mean that the drive was dieing.

As the Maxtor's drive was brand new (just out of the anti static bag) it could not be the case. After a test with a second 160GB drive the results were the same. Logically thinking - this means we have hit the LBA32 127GB limit. The BIOS cant address more address space than 127GB and when you do you hit the brick wall of buffer overflows in the address registers (most likely when you write over 127GB you start from the 0x0 h again and write up the drives beginning). Of course the Linux kernel takes over the drive addressing after you boot up, but for that to work well the BIOS has to be satisfied first. Well copying 127GB at the rate of 500KB/s would take 266 338 seconds - thats around 3 days straight - I didn't have that much time to wait to see what would happen after the limit gets exceeded.

So what to do when your hardware is too obsolete for upgrading to your needs? You hack it!

In my case it was simple as Maxtor has firmware utility called SeaTools that can change the drive capacity in the firmware. Why is that good you ask? Well this way we can fake the hardwares without using the soldering iron or assembler to hack the firmware in the device.

The procedure goes like this:
  1. install the new HDD
  2. boot into BIOS and accept the changes (new HDD 6GB?!?!?)
  3. boot into the SeaTools utility (CD or floppy)
  4. Change the drives capacity to be 32GB
  5. Shutdown the machine and remove the drive
  6. Boot into the BIOS and accept the changes (the IDE drive has gone away)
  7. Shutdown the machine and reconnect the drive
  8. Boot into BIOS and accept the changes (new 32GB drive)
  9. Boot into the SeaTools and restore the drives capacity
  10. Boot into Linux :)
The BIOS still thinks it has a 6GB drive connected but its happy with it. Also the Linux boots up faster as BIOS is not complaining about seek errors when addressing the drive.

Running hdparm  -t should result in 13...25MB/sec - not the best speed but a lot better than 500KB/sec. You may ask what the range is so big - but I don't have an answer. On some systems the drive runs with udma2 mode on others in mdma2 mode. Forcing the mdma2 mode to go to udma2 mode did not seem to have the desired performance change but still its working well enough.

Many may ask "why would you ever want to resurrect an old xSeries 220", but the answer is simple. The system has been in use for a long time and if it has not died so far it wont in the near future. Also the speed is boosted with built in SCSI drives.

So where to use the old xSeries 220? Well, for test servers, for low priority web/sql servers, dns servers - there is no good answer. It all depends on the needs of the system. One place would be central log server - aka other servers log to this host, the syslog would save the logs in real time to the SCSI drives and nightly you rotate the logs to go into the mysql database on the IDE drive. Why do this? Well, logs are here for one purpose to be analyzed afterwards.

Another good example would be to use it as a file server - share out the data on SCI to Linux hosts and from IDE to windows hosts and if they start to complain that the speeds are soooo slooowwww blame it on windows and propagate the move to Linux :P

What can I say - use Your imagination.
Tested on CentOS 4.5 - but should work on any Linux with 2.6 kernel.

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