[NTLUG:Discuss] Software RAID NAS Box

[Richard Geoffrion]

Daniel Hauck wrote:
> <snip the background to reduce the message burden on the list>
>
> Initially, I'm just thinking of mimicking the previous scheme when it was running under Win2K.  In this case, each drive will have the same partition scheme:
>
> 100MB /boot,
> 2GB {swap},
> 4000MB /
> *everything else* /data
>
> The non-swap partitions should be RAID
>
> <snip some more>
>
> Okay, so I'm soliciting comments and better ideas..?
>   
Um, Daniel, 

TERSE VERSION:  non-raided swap space puts the server at risk of a crash 
should a drive containing swap space fail.

VERBOSE VERSION: (in story form--should you choose to read the 
"fictional" {ahem} account that I spent entirely TOO much time writing.)

 From the pages of that horror story "My server crashed when a disk 
failed" let me recount the climax where the network administrator 
realizes too late the perils of non-RAIDed swap space.

---------------
"I though you said the system would survive a crash if a hard drive 
failed?  Isn't that why I bought multiple drives for my server?", 
inquired the customer.

"It should have.", mumbled the network administrator, "It should have 
survived the hard drive going down.  As a matter of fact, evidence in 
the logs point to a memory failure. Only, I ran a RAM test and the RAM 
tests clean."

Sudden realization filled the network administrator with dread - the 
mistake of good intentions realized. The mistake wasn't just on this 
failed server but on many of the servers.  Time bombs were ticking away 
in the server room. The network administrator's mind raced to put words 
to the issue.  Reluctantly the network administrator informed the 
customer as to the cause of the crash.

"In a sense, RAM is hard drive space because hard drive space is USED 
like RAM via the swap files.   When the hard drive went out, it took the 
swap file with it and thus the memory pointers of the processes that had 
been swapped out at the time.  It was in effect a lobotomy for the 
server, hence the crash?"

"Well, what needs to be done then?  Is using multiple drives useless?"

"Using multiple drives still gives you protection from drive failure, 
but we will want to RAID our swap partitions to protect the data they 
hold from a future drive failure."

"But won't that reduce the amount of swap space we have allocated and 
put a burden on our servers by reducing the memory available?" the 
customer asked in concern.

"Technically, yes.", mused the network administrator, "But the need for 
all that swap space isn't as critical in these days of increased 
physical RAM.  Except for tempfs.  We can no longer use tempfs for our 
/tmp directory.  Tempfs uses RAM -and thus swap space- to create a 
temporary filesystem like a RAM disk.  We'll need to be sure to deal 
with mounting /tmp in an appropriate place.   It looks like I'll be 
spending some time in the server room correcting these issues."

"Better you than me." said the relieved customer.  "I'll be thinking 
about you this weekend while you're working."
---------------

-- 
Richard