Converting from unRAID to Arch?

musasabi · 2011-09-01 18:18:46

So I've got a 5TB unRAID server at home. It's been a champion and I really enjoy having it.

The problem is that unRAID is fairly limited in terms of expansion. It's interface is somewhat awkward and package management is unwieldy. Needless to say, I want to convert it to Arch.

My query is, then, can I do this without losing data? I've got unRAID booting from a flash drive presently, and aim to boot Arch in the same fashion.

lilsirecho · 2011-09-01 19:40:46

My latest install is a boot from Compact Flash raid0 which performs very nicely with the latest linux kernel upgraded after initial install in kernel26 via ftp. I have 5 compact flash devices of 16GB each running at 306MB's read speed.

Arch will load from flash devices but the speed if using USB2 will be much slower than using Compact Flash as an IDE block device. With an IDE adapter to CF the speed is around 45MB/sec and with a sataII to CF adapter, the speed is ~65MB/sec for a single CF flash card. This is very comparable to a normal HDD.

Good luck with your efforts.

musasabi · 2011-09-01 19:48:09

That sounds like a cool setup. Thanks for the info.

My real curiosity is if I'll be able to mount the drives I've got now into an Arch install configured for RAID and they'll read properly. I'd love to not have to shuffle the files around for the OS change.

lilsirecho · 2011-09-01 20:47:22

The usual requirement for raid software is to use mdadm with command ..assemble... and the appropo set of drives as a target.

This entails having setup a raid(x) array at appropriate level and making the mkinitcpio adjustments as outlined in mdadm wiki.

Thus the array can be assembled during boot using /etc/mdadm.conf.

There should be no problem if mdadm was first employed to make up the raid array. My use of raid arrays allowed the use in more than one instance of archlinux hdd and flash device arrangements.

The uuid is used and the raid array device is ID'ed as raid and cannot be changed except by DD command.

musasabi · 2011-09-01 20:51:54

Fantastic. Thank you for the informative post. Does building the RAID array with mdadm destroy data?

filam · 2011-09-01 23:38:46

musasabi wrote:

Does building the RAID array with mdadm destroy data?

It may, which should be reason enough to back up your data.

You might want to read the Activate existing RAID devices and LVM columes section in the Installing with Software RAID or LVM article. Also, I'm currently rewriting that article here.

lilsirecho wrote:

There should be no problem if mdadm was first employed to make up the raid array.

musasabi, you should find out if this is the case with your unRAID array.

lilsirecho · 2011-09-01 23:39:18

Assembling a raid array does not destroy data. Creating, or building an array destroys data.

You will be asked if you are trying to do the rebuild.

Best process is to copy the data to a flash drive before you do any other thing.

I suspect the raid devices will be identified as raid devices when you ask for assembly with the mdadm command but have backups just in case. You cannot copy individual devices but the whole array for the backup....unless the raid array is compatible with such an approach. In raid0 which is striping, you cannot even mount the drives separately they are not recognized as mountable.

EDIT: I speak for mdadm procedures and have no knowledge of unRAID and assume that it has raid devices which mdadm should recognize. The actual raid level for unRAID is unknown to me and whether it is bootable and the processes for running it in an arch environment might be incompatible. Therefore, copy the raid data you need to have, probably none of the system params but your personal data is recommended. Attempting to run the raid array as provided by unRAID may not be possible as an arch bootable system. If it is not a bootable array, the array may be a success with mdadm assemble command after you are booted into archlinux.

EDIT#2:UnRAID

UnRAID is best compared with RAID 3/RAID 4, without striping. Data drives are kept in normal reiserfs format, but a 'smart' parity drive emulates the function that striping plays in RAID3 and RAID4 with a specialized data structure. Pointers on the parity drive combine files on the various drives into virtual stripes which then get parity data. Read checksum are checked against the parity checksum (and reconstructed if incorrect.) Writes create new parity information. The main advantages to this approach are: data drives are readable and writeable on any system, separated from their array—the system can fail without harming the array; different-sized drives can be combined; partial recovery is possible if the number of failures exceeds the number of parity disks (usually one).
Based on distributed, unsupported[23] GPL source code, UnRAID is suited to cheap, simple, expandable archival storage, similar to the more extreme write-once, read occasionally use case.
Disadvantages include slower write performance than a single disk, filesystem overhead (additional checksums are required to avoid querying the other disks to check the data disks in use), scaling problems, bottlenecking when multiple drives are written concurrently. UnRaid allows support of a cache drive (Plus and Pro versions) which dramatically speeds up the write performance. The data is temporarily unprotected until UnRaid automatically moves it to the array based on a schedule set within the software. The parity drive must be at least as large as the largest data drive to provide protection. UnRAID is implemented as an add-on to the Linux MD layer.[24]
[edit]

This indicates there may be data concerned with add-ons in the MD system...Look into that for aid. Raid3 or raid4 has been referred to as the comparable raid system ID as a possibility. The add-on mentioned needs some expanded insight.

EDIT#3: You probably have large drives associated with unRAID like maybe TB sizes/ lotsa videos , etc. You do not specify much in your posts.

Last edited by lilsirecho (2011-09-02 00:15:56)

Arch Linux

#1 2011-09-01 18:18:46

Converting from unRAID to Arch?

#2 2011-09-01 19:40:46

Re: Converting from unRAID to Arch?

#3 2011-09-01 19:48:09

Re: Converting from unRAID to Arch?

#4 2011-09-01 20:47:22

Re: Converting from unRAID to Arch?

#5 2011-09-01 20:51:54

Re: Converting from unRAID to Arch?

#6 2011-09-01 23:38:46

Re: Converting from unRAID to Arch?

#7 2011-09-01 23:39:18

Re: Converting from unRAID to Arch?

Board footer