Migration to RAID 1

deconstrained · 2009-09-01 23:33:19

I'm tentatively considering getting a second HDD of identical capacity and re-installing the kernel (adding "raid" to hooks?) to be configured for mirroring so that my data is a bit more secure and disk reads can go faster. Would this be feasible, and not terribly convoluted/requiring hacks or following very, very verbose instructions?

My current Arch installation is on a single 1 TB partition formatted as JFS. My motherboard supports RAID 1, so I'm not sure whether software RAID is necessary, or if it would get me better performance.

apollokk · 2009-09-01 23:40:23

Don't use RAID, especially in Linux.

Leave it in AHCI mode.

deconstrained · 2009-09-01 23:43:05

Will it cause problems in general, or is it a bad idea to try to move from an installation on a single disk to an install on a mirrored system?

apollokk · 2009-09-01 23:46:28

Even if it's said to be safe, it isn't.

Also, Linux, does not fully support it, and you'll met a lot of problems.

deconstrained · 2009-09-01 23:52:11

But...isn't it (mirroring) safer than just one disk? Also, I don't mean to be argumentative, but I was just wondering: what are you referring to by "not fully"? Does running on RAID under Linux have bugs and/or exhibit abnormal behavior? According to the Arch wiki there is a module available for RAID 1.

apollokk · 2009-09-02 00:06:30

I have seen a lot of problems with RAID and Linux.

Broken RAID arrays e.g.

fukawi2 · 2009-09-02 01:10:02

I'm not sure what experiences apollokk has had, but I've found Software RAID and Hardware RAID both to be very well supported in Linux.

I'm running Software RAID-1 on my home desktop and home server at the moment. I've previously used Hardware RAID in server environments including Adaptec and HP RAID controllers without issue as long as you make sure the particular card has Linux drivers -- some of the cheaper 'hardware' RAID device don't. Yes, it can sometimes be fiddly to get it going when you're trying to RAID your system disk, but once it's running it's good.

Using your motherboard's RAID might be a little bit more difficult -- I've found BIOS RAID to be flaky before. I'd go with Linux Software RAID over your motherboard's RAID (which is software too btw). Chances are there's more people using Linux Software RAID than there are people using your motherboard's RAID -- ergo you'll get more support.

Last edited by fukawi2 (2009-09-02 01:11:45)

deconstrained · 2009-09-02 01:24:38

Question: when you set up two drives in RAID-1, are they just carbon copies of each other (as I currently understand), e.g. bit-for-bit similarity, or do they require some kind of special treatment? If one dies, will I be able to use the other as if it were an ordinary disk (after reconfiguring the kernel, hooks, etc.)?

fukawi2 · 2009-09-02 02:42:39

Yes -- they are identical, and just 'normal' drives. mdadm just sets up an abstraction layer above the disks to ensure writes are sync'ed to both disks when they're mounted through mdadm as a single device.

If one disks fails, you can either:
1) Mount the mdadm RAID device in a degraded state until you can replace the failed drive; or
2) Mount the good drive as a normal /dev/sdXy (eg, /dev/sda1) device and forget about the RAID.

Option 2 will require you to recreate the RAID when you replace the drive and 'start from scratch' so to speak, so option 1 is probably more suited if possible. Of course option 2 makes it easy to put the drive anywhere and work with it without having to reassemble the array.

* everything above relates to RAID-1 arrays only. RAID-0, RAID-5, RAID-10 etc will not exhibit this behaviour due to striping, parity etc *

.:B:. · 2009-09-29 23:41:14

Applocker: there's no need for spreading paranoia. Keep in mind one's knowledge (or lack thereof) is instrumental in overcoming problems or (failing to) putting them in perspective.

Software RAID on Linux is reliable, I can't speak for hardware RAID, never used it.

Running a RAID 5 and RAID 1 here with mdadm on my server. Except for the RAID 1 being faulty after a hard reset, never had a problem. Resyncing the array fixed it.

iBertus · 2009-09-30 00:35:40

I've used software RAID in linux (via mdadm) for a few years now and haven't had any issues. My current array is 6x750GB drives in RAID5.

Arch Linux

#1 2009-09-01 23:33:19

Migration to RAID 1

#2 2009-09-01 23:40:23

Re: Migration to RAID 1

#3 2009-09-01 23:43:05

Re: Migration to RAID 1

#4 2009-09-01 23:46:28

Re: Migration to RAID 1

#5 2009-09-01 23:52:11

Re: Migration to RAID 1

#6 2009-09-02 00:06:30

Re: Migration to RAID 1

#7 2009-09-02 01:10:02

Re: Migration to RAID 1

#8 2009-09-02 01:24:38

Re: Migration to RAID 1

#9 2009-09-02 02:42:39

Re: Migration to RAID 1

#10 2009-09-29 23:41:14

Re: Migration to RAID 1

#11 2009-09-30 00:35:40

Re: Migration to RAID 1

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