Need Suggestions for Automated Backup

[Matthew Carpenter]

Thanks for the summary, Alma.  That's about how I recall it.  

On Wed, 03 Dec 2003 19:26:43 +0000
Alma J Wetzker <almaw at ieee.org> wrote:

> 
> 
> 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
> 
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> 


-- 
Matthew Carpenter 
matt at eisgr.com                          http://www.eisgr.com/

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