Here is my impression after using the RAID code for a few days on
2.4.0-test{7,8}... Forgive me if I speak something stupid.
1. There's not enough documentation.
The HOWTO only steps one through the most common operations.
Theoratically, it can be done by resizing the fs and adding a
superblock, no? Has a tool been made for this?
The HOWTO also doesn't tell you how to change your configuration.
Suppose I want to add a disk to a mirror set. Do I add it to
raidtab and mkraid again? Or do I raidhotadd it and then add it
to raidtab?
There are no section on converting an existing partition to RAID.
2. It's not robust against stupid users (i.e. me)
e.g. I cannot create a RAID1 with only 1 partition, running it like a
normal partition with intention to add a mirror later. mkraid seems to
allow it but the mirror thread hung trying to mirror the RAID.
3. Configuration is hard to manage.
As I said in (1), only the most common operations seems to be
supported. Anything else seems to be backup-remake-restore.
What if I want to add a disk to a RAID1 set, making the set RAID5?
Or adding a new disk to a RAID5 set for more capacity? I do not
know what the operation will do to the data in the partition.
There should at least be documentation for this.
In the least, there should be a tool to create raidtab from the
autodetect information. The HOWTO should also include information
on the effect of data in the partitions after changing RAID
configuration.
*** I understand that autodetect is experimental. But if you are
moving to that eventually may I suggest that you move to a new model?
Namely, that configuration be managed by tools rather than the raidtab
file.
For example, I think it is much more intuitive to
PreparePartition --name HOME-1 /dev/sda5 # create persistent superblock
PreparePartition --name HOME-2 /dev/sdb5 # ditto
mkraid --type RAID1 --name HOME --sub HOME-1 --sub HOME-2
raidstart HOME # creates /dev/md/HOME
mke2fs /dev/md/HOME
mount HOME /home
To add a mirror and a spare:
PreparePartition --name HOME-3 /dev/sdc5 --name HOME-SPARE /dev/sdd5
raidhotadd HOME --sub HOME-3 --spare HOME-SPARE
And maybe we can to convert it to a RAID5 like this:
umount /home
raidstop HOME
mkraid --type RAID5 --name NEWHOME --sub HOME-1 # Data is preserved
raidstart NEWHOME
raidhotadd --extend NEWHOME --sub HOME-2 --sub HOME-3 --spare HOME-SPARE
(output> old size is xxxxxx, new size is yyyyyy)
resizefs -t ext2 xxxxxx yyyyyy /dev/md/NEWHOME
Opinions welcome.
Regards
Stephen
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