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I need some comments in regars to my NAS. I have a Linux Server running Ubuntu 10.04 (may upgrade) and I have a RAID5 for my storage aray, it consits of 4 x 1.5 TB HDDs. OS is running on a seperate disk and I have a 1 TB USB drive that is currently empty.

I am thinking of "destroying" the RAID 5, to gain additional storage space, and start using MHDDFS to mount multiple drives too one mount point for a "large array". Today I loose 1 x 1.5 TB diskspace the the RAID 5. I do not want to run 1 large volume, because if I lose 1 disk, I lose it all.

Any comments in regards to using MHDDFS? I have never tried it before.

Also, any comments in regards to breaking a raid5 using that is setup with MDADM.

My plan is to:

1. Move 1 TB of data off the 4 TB raid 5

2. Remove 1 of the drives from the RAID5

3. Format the "broken" drive

4. Move 1.5 TB off the degraded RAID5

5. Reshape the RAID5 with 3 drives

6. Remove 1 of the drives from the "new" RAID5

7. Format the 2nd "broken" drive

8. Move 1.5 TB off the new degraded RAID5, which should be empty

9. Format the remaining 2 drives

10. Mount all drives using MHDDFS

Questions:

A. Is my plan viable (assumbing that I have enough data space available)

B. Am I risking all the data by breaking the drives (assuming no HW failures)

C. Comments in regards to MHDDFS

D. Can I mount multiple drives, with data, using MHDDFS to one mountpoint?

Any views and comments?

BTW: I do know that I will not have any redundancy any more, but the main point is not to lose ALL data if A SINGLE drive fails.

Thanks.

Ok, I solved the issue. Thanks to even more googeling, and a failed drive that "forced" me into moving on with this.

What solved it? Installing an experimental version of mdadm, allows the removal of a drive.

NOTE: This is an experimental case, so please do not run if you are not willing to risk data.

Links:

Blog Post with Howto

Ubuntu forum post about upgrading

Debian Package for mdadm

How to Resize RAID (tips only)

Here is my "solution":

1. 4 Drives in RAID5, 1 drive failed

Code:
cat /proc/mdstat

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]

md0 : active raid5 sdb1[0] sdd1[3] sde1[2]

4152360960 blocks level 5, 64k chunk, algorithm 2 [4/3] [u_UU]

mdadm --detail /dev/md0

/dev/md0:

Version : 00.90

Creation Time : Fri Apr 8 12:39:06 2011

Raid Level : raid5

Array Size : 4152360960 (3960.00 GiB 4252.02 GB)

Used Dev Size : 1384120320 (1320.00 GiB 1417.34 GB)

Raid Devices : 4

Total Devices : 3

Preferred Minor : 0

Persistence : Superblock is persistent

Update Time : Sun Sep 9 11:34:27 2012

State : clean, degraded

Active Devices : 3

Working Devices : 3

Failed Devices : 0

Spare Devices : 0

Layout : left-symmetric

Chunk Size : 64K

UUID : 3ce16aed:03b66e97:272fb3ce:18a82fda

Events : 0.310190

Number Major Minor RaidDevice State

0 8 17 0 active sync /dev/sdb1

1 0 0 1 removed

2 8 65 2 active sync /dev/sde1

3 8 49 3 active sync /dev/sdd1

2. Forced 3 of 4 drives online

Code:
mdadm --assemble --force /dev/md0 /dev/sdb1 /dev/sdc1 /dev/sde1 /dev/sdd1

3. Copied out data leaving only 1.3 TB on degraded RAID5

4. Resized /dev/md0 to 1.3TB instead of 4 TB

Code:
e2fsck -f /dev/md0

resize2fs /dev/md0 1300GB

5. Installed mdadm experimental

Code:
# wget http://ftp.se.debian.org/debian/pool/main/m/mdadm/mdadm_3.2.5-3_i386.deb

#dpkg -i mdadm_3.2.5-3_i386.deb

# mdadm --version

mdadm - v3.2.5 - 18th May 2012

6. Resize Array

Code:
# mdadm /dev/md0 --grow --array-size=1385120320

# mdadm --detail /dev/md0

/dev/md0:

Version : 0.90

Creation Time : Fri Apr 8 12:39:06 2011

Raid Level : raid5

Array Size : 1385120320 (1320.95 GiB 1418.36 GB)

Used Dev Size : 1384120320 (1320.00 GiB 1417.34 GB)

Raid Devices : 4

Total Devices : 3

Preferred Minor : 0

Persistence : Superblock is persistent

Update Time : Sun Sep 9 12:46:27 2012

State : clean, degraded

Active Devices : 3

Working Devices : 3

Failed Devices : 0

Spare Devices : 0

Layout : left-symmetric

Chunk Size : 64K

UUID : 3ce16aed:03b66e97:272fb3ce:18a82fda

Events : 0.310204

Number Major Minor RaidDevice State

0 8 17 0 active sync /dev/sdb1

1 0 0 1 removed

2 8 65 2 active sync /dev/sde1

3 8 49 3 active sync /dev/sdd1

7. Decrease number of drives

Code:
# mdadm /dev/md0 --grow --raid-devices=3 --backup-file=/tmp/mdadm.backup

mdadm: Need to backup 384K of critical section..

8. View new raid set

Code:
# mdadm --detail /dev/md0

/dev/md0:

Version : 0.91

Creation Time : Fri Apr 8 12:39:06 2011

Raid Level : raid5

Array Size : 1385120320 (1320.95 GiB 1418.36 GB)

Used Dev Size : 1384120320 (1320.00 GiB 1417.34 GB)

Raid Devices : 3

Total Devices : 3

Preferred Minor : 0

Persistence : Superblock is persistent

Update Time : Sun Sep 9 14:03:55 2012

State : clean, degraded, reshaping

Active Devices : 3

Working Devices : 3

Failed Devices : 0

Spare Devices : 0

Layout : left-symmetric

Chunk Size : 64K

Reshape Status : 0% complete

Delta Devices : -1, (4->3)

UUID : 3ce16aed:03b66e97:272fb3ce:18a82fda

Events : 0.310214

Number Major Minor RaidDevice State

0 8 17 0 active sync /dev/sdb1

1 0 0 1 removed

2 8 65 2 active sync /dev/sde1

3 8 49 3 active sync /dev/sdd1

8. Monitor progress

Code:
cat /proc/mdstat

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]

md0 : active raid5 sdb1[0] sdd1[3] sde1[2]

1385120320 blocks super 0.91 level 5, 64k chunk, algorithm 2 [3/2] [u_U]

[>....................] reshape = 0.0% (476800/1384120320) finish=3005.5min speed=7672K/sec

Now I just need to wait for 50 hours for the reshape to be done! Data is accessable still, so lets hope that nothing kills the data on the drive.

That's... a pretty comprehensive guide!

Yeah, I was surprised to see I could run "pvcreate" against my mirror array whilst it was still being built. I created LVs, put filesystems on them, mounted them and restored data... all whilst /dev/md0 was still synchronising. Fantastic!

chj

chj

Dungeon-Dave