Hi,
I was just thinking about the following :
There will soon be available at least one stable journaled FS for linux
out of the box.
Of course we want to run our soft-RAID5 array with journaling in order
to
prevent large fsck and speed up the boot process.
My question:
what happens when I run RAID5+ jornaled FS and the box is just writing
data
to the disk and then a power outage occurs ?
Will this lead to a corrupted filesystem or will only the data which was
just written,
be lost ?
I know that a single disk + journaled FS do not lead to a corrupted
disk,
but in the RAID array case ?
The Software-RAID HOWTO says:
"In particular, note that RAID is designed to protect against *disk*
failures, and not against
*power* failures or *operator* mistakes."
What happens if a new written block was only committed to 1 disk out of
4disks present in an array (RAID5) ?
Will this block be marked as free after the array resync or will it lead
to problems making the
md device corrupted ?
If the software RAID in linux doesn't already guarantee this, could
this be added with a similar technique
just like a journaled FS does ?
I am thinking about keeping a journal of the committed blocks to disk,
and if a power failure occurs, then
just wipe out these blocks and make them free again.
A journaled FS on top of the raid device will automatically avoid files
being placed in these
"uncommitted disk blocks".
But since md is a "virtual device" the situation might be more
complicated.
I think quite a few of us are interested this "raid on powerfailure
during diskwrites reliability" topic.
Thank you in advance for your explanations.
regards,
Benno.
