Author Topic: expanding hard drives / RAID question  (Read 1190 times)

brake16

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expanding hard drives / RAID question
« on: June 02, 2009, 08:58:33 pm »
Good Morning

I'm curious if the following would work:

I currently have an 80GB SATA hard drive in the hybrid for the LMCE system.  I'm going to add more hard drives for media.  I'd like to eventually setup a RAID 5 using multiple 1.5 TB disks.  To spread out the cost and to minimize the chance for a 2-drive RAID5 failure (due to similar aged drives), I'd like to purchase and install the drives about 4-6 months apart.  I'm aware that I'll be running "at risk" the first 4-6 months with only 1 drive, but that's also the least likely age-related-failure window.

So, I know I can put in the first drive and LMCE will use it just fine.  When I add the second drive (4-6 months later) is it possible to then setup both drives as RAID1 without data loss on the first?  Then again, when I add the third drive, is it possible to setup all 3 drives as RAID5 without data loss?

Please note, I'm aware of the risk of messing with drive structure when you want to preserve data.  Again, I am aware the I could lose my data during the upgrades.  But before I start down this road, I'd like to know if it can work.

I've found that it is possible to expand the RAID5 after it's setup (http://wiki.linuxmce.org/index.php/Grow_Raid, and http://forum.linuxmce.org/index.php?topic=4377.0).  Is it possible to grown into a RAID5?

Thanks
Bryce
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merkur2k

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Re: expanding hard drives / RAID question
« Reply #1 on: June 02, 2009, 09:47:07 pm »
No, it is not possible to change a raid array in any way without having to rebuild the array (which is a destructive process). if you insist on using raid, you will have to backup the data each time you make a change.
since youre concerned about this, i am going to assume you dont have a working backup solution. its been said before and will be said many more times i am sure: a raid setup does NOT negate the need for backups! you are better off in the long run just adding drives jbod and letting the backup system do its job if/when there is a failure.

Zaerc

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Re: expanding hard drives / RAID question
« Reply #2 on: June 03, 2009, 01:30:37 am »
In theory it should be possible to build a degraded RAID-5 array out of two drives, copy the data over from the third and then add it to the array.

In reality (and if you value your data): what merkur2k said above.  And just because it cannot be said enough:  RAID  is  never a  good  substitute  for  backups.  I wouldn't use JBOD though, but that's just me.
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posde

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Re: expanding hard drives / RAID question
« Reply #3 on: June 03, 2009, 08:45:27 am »
Just some tidbits of real life happenings:
I started out with a RAID 1 (a mirror) on one of my Linux machines. Bought a couple of new drives, and did not have enough SATA ports. I created a RAID 5 with two drives, copied over all the stuff from the RAID 1, took out the old RAID 1 drives, added two new drives to the RAID 5, and now have three active disks in my RAID 5 plus a single hot spare for my system, in case problematic things happen.

It did take some time, but it was a straight forward process.

With LinuxMCE and the changes jondecker did to the RAID part of the system, things like managing RAID 5 within LinuxMCE became much easier. Still, as both merkur2k and Zaerc have pointed out, it is not a backup solution. For me, RAID 5 is a solution which keeps my system running in case a single drive failure happens, so I can work a bit longer, get replacement drives etc. For data I have a backup, for media data I do not.

wierdbeard65

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Re: expanding hard drives / RAID question
« Reply #4 on: June 03, 2009, 09:55:19 am »
I created a RAID 5 with two drives
Can you do this? I always thought you needed a minimum of 3 drives for Raid5. This is useful stuff as, in the long run, I want to put in some serious disk space but don't want the grief from the family if I lose a drive with their fave episode of "The Simpsons" or whatever on it. If I can start with 2 drives and then keep addidng as finances permit (and to stagger the commission dates), that would be helpful. Knowing LinuxMCE can expand the arrays on the fly is also good to know.

Care to write a wiki on the exact process for morons like me who need it spelt out for them?  ;D
Paul
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posde

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Re: expanding hard drives / RAID question
« Reply #5 on: June 03, 2009, 11:31:50 am »
You can create a RAID 5 with two drives. That RAID 5 is in a broken state, but you are able to read and write files. There are lots of how-to's floating around, just google for How To RAID5 Debian and you shall find lots of information.

wierdbeard65

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Re: expanding hard drives / RAID question
« Reply #6 on: June 03, 2009, 11:33:51 am »
You can create a RAID 5 with two drives. That RAID 5 is in a broken state, but you are able to read and write files.
Ahh, I see! Is there a performance hit with having a "broken" Raid5 (like does it fill the logs up quickly?)
There are lots of how-to's floating around, just google for How To RAID5 Debian and you shall find lots of information.
Will do!
Paul
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merkur2k

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Re: expanding hard drives / RAID question
« Reply #7 on: June 03, 2009, 04:27:21 pm »
a raid array operating in "degraded" mode takes a pretty serious hit to read/write performance.

Pnuts

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Re: expanding hard drives / RAID question
« Reply #8 on: June 03, 2009, 09:38:22 pm »
Would it be bad to install using the alternate cd and create a raid partition then? Afterwords performing the install as normal?

I just did a clean 8.10 install this past weekend and haven't had a chance to do anything other then the initial wizards following the install. I planned to get my HDHomerun, Z-Wave and an MD going this weekend, but would I be better off reinstalling the correct way?

I have a NAS with all of my data and media that is important, I just wanted to increase disk IO on the core for recorded TV and such. I setup a RAID 0 with the only 2 disks in the system.

-Pnuts

posde

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Re: expanding hard drives / RAID question
« Reply #9 on: June 03, 2009, 10:00:17 pm »
pnuts,

do an install using the desktop CD, and configure your data HDD later on.

Pnuts

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Re: expanding hard drives / RAID question
« Reply #10 on: June 03, 2009, 10:19:35 pm »
pnuts,

do an install using the desktop CD, and configure your data HDD later on.

what I mean is, I wont stick any data at all on the core (except recorded TV from myth). All of my data will be on the NAS.

I just did it for disk IO so I don't bottleneck at hard drive read\write if say recording many shows while also watching many recorded TV at the same time and because I thought Alternate CD was the same as Desktop version just without the GUI and being more configurable during install.

I guess ill start the weekend off with a reinstall.

1 side question, How would I go about having a newer e1000e driver included with the final 810 DVD? I have to update it after Kubuntu installation as the included one does not support some PCI-E cards.

-Pnuts