Need Suggestions for Automated Backup

[Alma J Wetzker]

Matthew Carpenter wrote:
> From: "Net Llama!" <netllama at linux-sxs.org>
>>Its worth noting that RAID5 is generally alot slower than RAID0 or RAID1.
> 
> 
> That's not been my experience.  Using hardware RAID at least, RAID1 is much
> slower than RAID5.  RAID0 doesn't count since it is only used for speed and
> doesn't provide data-protection.  In that way, RAID0 is a misnomer.
> RAID1 is a mirror, so the data is being written and read much like a
> standalone drive, assuming you have a separate controller for each drive.
> If both drives are on the same controller RAID1 is even worse.  RAID5
> spreads the data out so reads are (can be) much quicker than a RAID1 as
> multiple tracks can be read at virtually the same time.  Writing is similar.
> 
> I'm not sure how SW RAID5 compares to SW RAID1.

Please correct me if I am wrong, I have been out of this stuff for a few years.

I don't know of anyone using just RAID1 or just RAID0.  The installations that 
I know/knew about used RAID (10) or mirrored stripes.  That puts lots of 
spindles over your data for very fast reads and writes.

RAID 5 is strips with checksum.  That allows a single drive in the array to 
fail and you still get all your data.  If you have hot pluggable drives, you 
can replace a failed drive on the fly.  The reads are not quite as fast as 
RAID (10) because you only have half the spindles.  The writes are much slower 
because you need to generate the checksum for the file.  If you are updating a 
database, the files can be large and the checksum calculation long also.

If you do this with software rather than hardware, your OS will incur a huge 
performance hit with RAID 5 because of the checksum issue.  (You need to read 
the entire file for every update.)  Also remember that IDE drives have the 
basic inteligence of a floppy drive.  If you want optimized retrieval at the 
hardware level, get SCSI.

My experience is that doing this stuff in hardware is best, (Duh!) and that 
RAID 5 reads data about as fast as RAID (10).  The selection criteria then 
becomes what is more important, write speed (with cost) or just uptime of the 
array (cheaper).  NOTE: Both are faster on reads than a single drive alone.

I know everyone knows this but this time I knew it too ;)

     -- Alma