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Old 02-24-2005, 08:43 AM   #1
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Software RAID5: HDD lights always on

Hello! I'm pretty much a Linux newbie, though I work with a lot of students that are pretty hardcore. Please excuse me if I don't get all of the terminology right.

I'm setting up a web server at work on an oldish Compaq Proliant 1850R server. The machine has 4 hard drives:

0 - 9.1 GB Ultra SCSI2
1, 2, 3 - 146.8 GB Ulstra SCSI320

These are all sled-mounted, hot swappable drives, each with its own set of status lights. No worries about improper wiring on the activity lights, or anything like that.

We installed Gentoo (kernel 2.6.10 hardened r3) on the machine without any problems. We're using the 9.1GB drive for the boot partition, swap, and the root partition.

We set up a software RAID5 on the other three drives. That was also no problem at all - we followed an online how-to guide, then verified that we ended up with the same setup as on another similarly configured machine. The RAID seems to be working fine - it test out correctly, can be stopped and started correctly, can read and write files, etc.

Here's the problem - whenever the RAID is started, the individual drive activity lights on the three RAID drives are on constantly, as is the master system drive activity light. The drives don't sound like they're actually doing anything, the lights are just on constantly. If you stop the RAID, the lights turn off. If you start the RAID, they come back on.

The system drive (the 9.1GB) does not show this behavior - its light behaves as a HD activity light should.

So, I'm a bit concerned about the RAID drives - is there a problem that would affect the reliablity of the server or the integrity of the data we're going to put on the RAID? Any advice about how to debug this problem or what might be causing it is welcome.

Old 02-24-2005, 10:46 AM   #2
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An update...

Well, it appears that whatever the problem was, it resolved itself overnight.

This morning, the lights are behaving as I would expect them to. I stopped and restarted the RAID, wrote some data to it, etc., and everything looks OK. I'm still curious what might have been going on last night, but it appears that there's no major problem.

Old 09-22-2005, 09:17 AM   #3
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This is due to the fact that when a new raid5 array is created, it syncs the parity bits.

So it basically has to go through the whole drive as if it were in degraded mode and rebuild the parity. The drives had activity, and thus that's why you had the activity lights being on.

It takes about 6 hours on a .75 TB array.
Old 09-22-2005, 10:25 PM   #4
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Just to note

For a web server, it is better to use RAID 1 (mirroring) because it can access two or more files at once instead of one at a time that RAID 5 does. RAID 5 does well when writing and reading large files (+100 MB) at a cost of accessing multiple files at once.


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