[vdr] Re: Disk performance (was: vdr - some general questions)

[Emil Naepflein <Emil.Naepflein@philosys.de>]

On Fri, 26 Apr 2002 12:03:42 +0200, Axel Gruber <axelgruber3@gmx.de>
wrote:

> The Problem with a SOFTRAID (please correct me if i´m wrong)  is that is not simple to
> easy add a aditional device to the RAID so you have delete it all and create a new RAID (as i know)

Axel, I use the MD driver with Raid5 since more than one year now and
have upgraded to more disks multiple time. I even have done this without
much downtime for VDR during reconfiguration. The trick is to have at
least so many similar sized Raid5 partitions as you have maximum number
of disks so that there is always enough space to move old data around.

Example:
The maximum number of disks I could connect was 7. So I started with 3
80 GB disks having 7 similar sized partitions each having a size of
about 10 GB. The rest of the disk was for other uses, like root, usr,
home and var which are all mirrored, and some extra space for other
things. I started with 7 Raid5 partitions having each 30 GB of space.
Now I added another 80 GB disk. This disk was partitioned like the
others with 7 10 GB slices. Now I moved the files from the Raid5
partition with the lowest usage to some of the partitions on the new
disk except the one which has the same slice number. After that I
reconfigured this Raid5 slice now to contain all 4 disks, made a new
files system on it and voila, I had 40 GB on this slice now. I copied
back all the files and was finished. Actually I saved some time by not
copying the data to the new disk. I copied single directories to already
upgraded partitions with available free space and reconstructed the
symbolic links with an automatic procedure. This saves some time.
I repeated this for all the slices and was finished within one weekend.
This only took so long because copying around so many GBs takes time.
But I could view and record on VDR during the same time. :-)
I repeated the same procedure later again after adding another 3 Maxtor
disks.

So I think, software Raid5 is the most flexible thing you can use. You
can make all changes online. Raid5 already saved me from a data loss
because one Maxtor failed because of to much heat. The system still
worked fine. I replaced it and after online reconstruction, which may
take some time (I limited the reconsturction speed to about 3 MB/s to
avoid problems with recordings) everything was fine again.

Emil