[CentOS] software raid

Les Mikesell lesmikesell at gmail.com
Thu Mar 29 22:49:02 UTC 2007

Joshua Baker-LePain wrote:

>>> Would that I had the money to and still get the space I need.  Even 
>>> doing 2 12 disk RAID6 sets (each with a hot spare) gets you 9TB which 
>>> is 50% more space for the same money as RAID10.
>> You are omitting the cost of the raid controller here. For your 12+ 
>> ports you don't have much other choice except a dedicated network 
>> device.  For the size
> What do you mean by a dedicated network device -- do you mean a NAS?  
> Not true.  See, e.g., 
> <http://www.siliconmechanics.com/i10219/amd-storage-server.php>.

>> that normal people need - or that you might use on other machines, you 
>> might
> Are you implying I'm not normal?  ;)

9 TB in one box seems a little extreme.  My storage is a little more 

>> have the option of running raid10 (or 0 + LVM) in software on the 
>> motherboard ports plus some dumb $20/port cards and buying several 
>> extra drives.
> On that note, what cheap add-in SATA controllers have folks had good 
> luck with?  I haven't tried *too* hard, but the couple I've tried were 
> far less than stable.

I have a 4-port promise SATA card that seems OK but I haven't really 
used it that much.

> There is one advantage of hardware RAID that hasn't been mentioned yet, 
> and that's hot-swap.  Last time I tried, software RAID fell over when a 
> HDD suddenly disappeared.

I've had very good luck with hot-swap scsi drives with software raid. 
One box last booted in mid-2003 has had a couple of drives replaced and 
re-synced with no interruption in service.  (An IBM netfinity running RH 
7.3 if anyone cares).

With parallel IDE a drive failure has a fair chance of locking up the 
controller and any other drive on the same cable but SATA shouldn't have 
that problem.

As a counterpoint, with software raid you can mirror to about anything 
of the same size, not just something in the same box from the same 
vendor.  As an example, I have one server with a pair of internal IDE 
drives mirrored with a third 'missing' member and can connect an 
external firewire drive, sync it in, then remove it without shutting 
down.  You could also mirror to iscsi partitions on another machine if 
you wanted.

   Les Mikesell
    lesmikesell at gmail.com

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