[ale] Home Data Server Project

[Pat Regan]

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On 02/24/2010 10:35 AM, Brian W. Neu wrote:
> restoring from a backup.  I too love the 3ware cards, but you might be
> be just as good spending a little extra on your processor and going w/
> md raid 6.  

CPU horsepower for software RAID 5 and 6 hasn't really ever been an
issue.  My C2D 1.6 ghz laptop can compute RAID 6 at nearly 6 GB/sec.
Even 10+ years ago desktop and server CPUs were way outpacing the slow
processors on RAID cards.

Hardware RAID is a bigger win when mirroring is involved, especially if
you have a large number of drives in a RAID 10.  Hardware mirroring
requires only half the bus bandwidth.  Software RAID 5 or 6 only adds
one or two extra drives worth of bandwidth.  I used to run software RAID
5 on a 3ware 7800 card in my old dual Athlon XP desktop.  It was MUCH
faster and more responsive than hardware RAID 5 on that card.  It was
also much better than using the on board IDE controller.

Software RAID is also more flexible since you RAID on the partition
level.  I have a software RAID 5 that has been growing over the years.
It started life as 4 400 GB drives, then grew to 6 drives.  They're all
connected to the motherboard's 6 SATA ports.

When I ran out of space on the original drives I started adding 1000 GB
drives.  At the moment I'm running a RAID 5 on the first 400 GB of each
disk.  I'm low on space now and I will be replacing one of the 400 GB
drives with another 1000 GB drive this week.  My plan is to start up a 3
disk RAID 5 over the remaining 600 GB of the larger drives.

The "original" 6 drives gives me about 2 TB.  The new smaller 3 drive
RAID will give me an additional 1.2 TB.  Each of the next 3 disks I
replace will give me an additional 600 GB each for a total of 1.8 TB.

The next 3 drives will likely be 2 TB so I can start this slow growth
process all over again...  It's no Drobo, it isn't automated, but I have
the know-how to make it happen.

Rebuild times are starting to worry me a bit.  With 400 GB they rebuild
in way less than 2 hours.  My math tells me that the 1 TB drives will
take a good bit over 3 hours to rebuild.  That's a long time, but much
less time than it takes me to pick up a replacement drive.  I don't keep
spares around the house :).

Pat
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