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List:       linux1394-user
Subject:    Re: Linux1394-user digest, Vol 1 #1020 - 4 msgs
From:       AndyLiebman () aol ! com
Date:       2004-02-27 8:53:18
Message-ID: 1ac.20d3aeac.2d70a5ce () aol ! com
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In a message dated 2/26/2004 11:16:42 PM Eastern Standard Time, 
linux1394-user-request@lists.sourceforge.net writes:

     But regardless how it turns out, the fact that you absolutely
     need serialization for RAID independently from the particular
     hardware is something you should perhaps better post again at
l    inux1394-devel.

Stefan, 

I should just point out that you don't absolutely need serialization for 
RAID1 and RAID5. As I said previously, I have two 5-drive RAID5 arrays running on 
a Mandrake 9.2 system right now without serialization. But every 8 or 10 weeks 
or so, I get one of those freeze ups of a single drive. This always occurs 
when the system is under extreme I/O stress. I don't lose data -- I just have to 
restart my server and resync the RAID array(s). 

However, without serialization, I can never resync my 2 arrays 
simultaneously. I will get that freeze up within seconds of starting the second resync 
process. The same holds true for resyncing RAID1 arrays. Can only do one at a time. 
I haven't tried WITH serialization. I can't afford to lose the data on my 
drives. But I'll try to do the test on another system. 

Finally, without serialization, it has been essential that each drive in a 
RAID5 or RAID1 array be plugged into a different PCI card (Firewire channel). If 
I try to put two drives from a single array on the same channel, I also get 
the freeze up. I don't know if serialization will resolve this problem. I think 
this problem is related to the "resyncing two arrays at a time" problem; 
remember, I have 5 PCI cards and two 5-drive arrays. Each PCI card is connected to 
one drive from each array. So, if I try to resync both arrays, there is huge 
I/O stress occurring on each card. 

Under normal operation, having one drive from each array hooked up to each 
PCI card hasn't been a big problem. So, serialization isn't absolutely 
essential. But without it, things seem to be more delicate. I do get that freeze up 
once in a while. 

On another matter, you suggested that I post this issue (the whole thread?) 
on the linux1394-developer's list? Should I just make one long posting with all 
the comments that have been made about this issue? Don't the people on that 
list get the postings on the user lists too? 

Andy


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