How many RAID devices can you define?

How many RAID devices can you define?

[Robert Washburne]

I am setting up a file server using Gentoo 2005.1, kernel 2.6.14-r2

The installed system creates eight RAID devices - /dev/md[0-7], /dev/md/[0-7]

I wish to create nine RAIDs, so I used "mknod /dev/md/8 b 9 8" to create another
device (and its associated link, /dev/md8).

The hardware consists of a 650 MHz AMD Duron with 1 GB ram.  Four WD 250 GB IDE
drives are connected to the four IDE busses of two Promise Technologies IDE
ATA100 controlers.  The drives are all partitioned the same using partitions
[1-3, 5-12].

I used raidtools to define and create the RAIDs.

The first eight devices created and synced with no problem (seven RAID5 and one
RAID0).  But when I created the ninth RAID5, it got about 30% through the sync
and then the system hung.  Keyboard was dead.  I had to power-cycle.

The the system came back up, it continued to sync, but hung again after a minute
or two.

Is there a hard limit of only eight RAID devices?

If so, can this limit be readily increased?

If need be, I can repartition my drives and reduce the RAIDs to only eight, but
I would prefer to keep the nine, if possible.

Thanks in advance!

Bob W.

Re: How many RAID devices can you define?

[Max Waterman]

I did a /dev/MAKEDEV md and it seemed to create lots of /dev/md* devices :

/dev/md0   /dev/md17  /dev/md25  /dev/md5     /dev/mdsp13  /dev/mdsp7
/dev/md1   /dev/md18  /dev/md26  /dev/md6     /dev/mdsp14  /dev/mdsp8
/dev/md10  /dev/md19  /dev/md27  /dev/md7     /dev/mdsp15  /dev/mdsp9
/dev/md11  /dev/md2   /dev/md28  /dev/md8     /dev/mdsp16  /dev/mdspstat
/dev/md12  /dev/md20  /dev/md29  /dev/md9     /dev/mdsp2
/dev/md13  /dev/md21  /dev/md3   /dev/mdsp1   /dev/mdsp3
/dev/md14  /dev/md22  /dev/md30  /dev/mdsp10  /dev/mdsp4
/dev/md15  /dev/md23  /dev/md31  /dev/mdsp11  /dev/mdsp5
/dev/md16  /dev/md24  /dev/md4   /dev/mdsp12  /dev/mdsp6

/dev/md0 was already defined (I'm using it), but I don't have a /dev/md/ 
directory....perhaps that is a difference between Gentoo and FC4 (what 
I'm using)...

hth

Max.

Robert Washburne wrote:
> I am setting up a file server using Gentoo 2005.1, kernel 2.6.14-r2
> 
> The installed system creates eight RAID devices - /dev/md[0-7], /dev/md/[0-7]
> 
> I wish to create nine RAIDs, so I used "mknod /dev/md/8 b 9 8" to create another
> device (and its associated link, /dev/md8).
> 
> The hardware consists of a 650 MHz AMD Duron with 1 GB ram.  Four WD 250 GB IDE
> drives are connected to the four IDE busses of two Promise Technologies IDE
> ATA100 controlers.  The drives are all partitioned the same using partitions
> [1-3, 5-12].
> 
> I used raidtools to define and create the RAIDs.
> 
> The first eight devices created and synced with no problem (seven RAID5 and one
> RAID0).  But when I created the ninth RAID5, it got about 30% through the sync
> and then the system hung.  Keyboard was dead.  I had to power-cycle.
> 
> The the system came back up, it continued to sync, but hung again after a minute
> or two.
> 
> Is there a hard limit of only eight RAID devices?
> 
> If so, can this limit be readily increased?
> 
> If need be, I can repartition my drives and reduce the RAIDs to only eight, but
> I would prefer to keep the nine, if possible.
> 
> Thanks in advance!
> 
> Bob W.
> 
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