Problem with post-Installation RAID 0 for two HDD (SATA)

[Farrukhjon]

Hi guys!, A have problem with post-installation RAID0 for my two SATA HDD. In partition step i choose configuration RAID0, success create RAID MD0:
MD0 / 312 gB
/dev/sda1---swap
/dev/sda5---/ (boot)
/dev/sdb1---swap
/dev/sdb5---/ (boot)
When i logged as root and try:
grub-install --no-floppy /dev/sda
grub-install --no-floppy /dev/sdb
for degraded booting but the console print I/O error f0 --missing...and more info...
Help me , where i have do wrong.

[Hedgehog1]

Raid 0, or striping look like this across two drives:

http://upload.wikimedia.org/wikipedia/commons/thumb/9/9b/RAID_0.svg/150px-RAID_0.svg.png

Once the set up, the two 'striped' drives need to present themselves as a single 'larger' drive.

So a RAID0 of two 160 gig drives would appear as a single 320 gig drive (/dev/sdb).

Your setup:


MD0 / 312 gB
/dev/sda1---swap
/dev/sda5---/ (boot)
/dev/sdb1---swap
/dev/sdb5---/ (boot)

should really look like this:

/dev/sda <- tiny boot & OS drive (Possibly SSD?), 20-40 gigs
/dev/sdb <- Stripped set of RAID0 drives, which holds '/home/ & 'SWAP'

What RAID card are you using to make the RAID0? Do you have a separate boot drive/SSD?

The Hedge

:KS

[Farrukhjon]

I'm using mdadm, ie software RAID and i guide using this tutorial https://help.ubuntu.com/community/Installation/SoftwareRAID

[Hedgehog1]

Ahh yes.. Software raid...

The guide indicates that:


Warning: the /boot filesystem cannot use any softRAID level other than 1 with the stock Ubuntu bootloader

If you are booting from the SOFTWARE raid, you must use RAID 1.

Are you booting from the software RAID?

The Hedge

:KS

[Farrukhjon]

Yes i use sofware RAID, and i need to up degraded boot in my case :
two hdd (sda and sdb) each hdd have size of 160 gb and md0 uped each /dev/sdX have boot flag. But i whant boot my system if my first hdd would be halt down. Recomend me how do it.

[Hedgehog1]

The least-painful way is this:

3 drives; the two SATA drives you already have, and a small SATA drive

/dev/sda <-- small SATA drive, Mounts '/' & (and therefore '/boot', too)

/dev/sdb & /dev/sdc (they make up your RAID, and mount '/home' & 'SWAP'

This gives you a predicable boot drive (one small SATA) and the RAID for speed.

The Hedge

:KS

p.s. According to the Guide, they suggest 2 RAIDs, a little RAID 1 to boot, and then your RAID 0,5 or 6 for bulk data storage.

[Hedgehog1]

By the way, you likely already know this, but just in case:

RAID 0 is fast, but very risky. If any one drive fails, all data is lost.

RAID 1:

http://upload.wikimedia.org/wikipedia/commons/thumb/b/b7/RAID_1.svg/150px-RAID_1.svg.png

Will give your even better Reading performance, but slower Write performance. However, it will survive a hard drive failure.

It does mean you need two 320 gig drives to get a 320 RAID 1. But it is really worth it.

Also, software RAID is fine for learning. Hot-swappable hardware RAID is the best choice for critical servers.

The Hedge

:KS

[Farrukhjon]

Can i remove my MD0 RAID device without loss my data and recreate new RAID1 for mirrorize and degraded boot ? for example:

mdadm --create /dev/md0 --chunk=64 --level=raid1 --raid-devices=2 /dev/sda1 /dev/sdb1

[Hedgehog1]

Can i remove my MD0 RAID device without loss my data and recreate new RAID1 for mirrorize and degraded boot ? for example:

mdadm --create /dev/md0 --chunk=64 --level=raid1 --raid-devices=2 /dev/sda1 /dev/sdb1

Yes - this is a very good solution using the hardware you have on hand. It will give you a 160 gig RAID, and it will boot and still be a RAID.

The Hedge

:KS

p.s. The reason the software raid needs RAID1 is that right as it boots, it really uses /dev/sda by itself to boot, so that disk needs to be 'complete' and not striped.

[Farrukhjon]

Thanks, i would try it, and thank you very much, i glad that discuss with you. Good luck!

[Hedgehog1]

We are here if you need us again! Drop in any time...

Best of luck!

The Hedge

:KS