On Thu, Sep 11, 2003 at 12:19:59PM +0800, Fritz Mesedilla wrote:
> Hey Jijo! Long time no hear. :D

:)

> Actually, the IBM person who services us recommended raid 5 and
> proceeded to configure the servers for us. hehehe!

While I admit that most often than not I'd rather do things and let
people watch, I don't think that sort of thing really works. "Teach a
man how to fish", they say. Oh well, it's up to you to learn, then.

> After this only 4 drives are read by the IBM SCSI manager as 1 logical
> drive while the other 1 drive is considered swap drive. *scratches
> head*
> 
> Does this mean 4 drives are doing the parity thing of raid 5 while the
> 5th one is ready for swapping? Sabi lang kasi ng IBM tech ready for
> failover na yan.

This means that you have a four-drive RAID-5 array, with one drive on
standby as a hot-spare. It's ready for failover, meaning if a drive
crashes, the system will automatically rebuild the array using the
hot-spare, which, as I said in the previous email, allows you to get out
of degraded most in the fastest possible time. The bummer with that is
you've got a drive doing nothing most of the time.

> Medyo takot lang ako kasi hindi ako yung gumawa ng raid. :D If
> something happens tapos hindi ikaw yung tumira parang kabado ka di ba.
> Nangyari na kasi dati IBM tech din yung nag configure ng raid 5 test
> server namin tapos 1 drive failed, hinugot ko para palitan...
> nag-crash yung control... parang nalito yung controller. hehehe. I had
> to rebuild linux install again. The tech guy had to come back and
> flash the scsi controller.

That sort of attitude (that you have) is what gets people to learn a new
thing every day. The problem before had nothing to do with hot-spares or
RAID-5, though. It had everything to do with a flakey controller BIOS,
that the tech guy flashed. So much for love. Kaya nga sabi nila, hindi
purkit naka-RAID ka na eh wala ka nang backup. If you value your data,
back up (is what they always say). :)

> So I was wondering why it didn't work for me when I tried hot swapping
> it. Baka may tama lang yung scsi controller?

Yup! Hence the controller BIOS upgrade.

> Ok so tama ba ganito? Basta raid 5 hot swappable yung scsi I can just
> remove the drive and replace it?

It has nothing to do with RAID-5. If your controller supports
hot-swapping, you can remove the drive, replace it, and rebuild the
array all in real time. I do this with my 3ware Escalade, too, which
does hardware IDE RAID. You can employ any RAID level you wish and still
have a hot-spare if you want and still do hot-swapping if you want.
Well... except for RAID-0, since there's no redundancy there.

As I said in my previous email, I highly recommend you consider RAID-10
over RAID-5. At the expense of a little usable space, you get better
performance and more reliability. You can keep that hot-spare, too, for
even more reliability. :)

 --> Jijo

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