SCSI interface cards.

Roger Heflin rogerheflin at gmail.com
Thu May 1 15:01:57 UTC 2008


gary artim wrote:
> Hi Rodger --
> 
> Thanks for the quick responses. The backup unit is a Overland arcvault
> 12 w/lto4 drive. The lto4 have,
> I think, 120MBps (Native)/240MBps (compressed), so no gain using U320
> interface? I'd guess the max thru put
> would be 120MBs, with the compressed rate just accomplished because of
> data compressing. Sorry to
> be thinking out loud here, but this does help!
> 
> 
> -- G
> 

Well, if that is what you have, you did spend some decent money on it.

The important part it LTO4.   Native speed is 432GB/hr, or 120MB/second, if you 
get good compression and you have a *FAST* disk subsystem, then you could use 
that speed, I would test doing a backup with you backup software to /dev/null 
and see what the actual disk speed is, if you are backing up a lot of small 
files you won't be able to use all of the speed, or if the files are fragmented 
on disk you may not be able to use that speed.

If you data does not compress good you won't be able to go over 160 MB/second 
either.

You would have to be getting the data locally from a high-end disk subsystem, 
and you have to have big files, and you would have to data that was 
compressible.    Overall you have to be pretty careful to get something that 
will read at 120MB/second and also write out to a tape at 120MB/second, you have 
to make sure the PCI-X slots are not shared with each other, and that all other 
subsystems can do it.

And if your current SCSI card is PCI (not-X, not-64bit) then the actual limit
is probably < 132MB/sec (PCI limit).

I would try what you have and see what speed you are getting, if you run within 
20-30 of the limit you may be hitting the limit, if you are much below that you 
have other issues.

Generally though I have had good luck with the LSI cards, I have used their 
SCSI, SAS, and fiber channel cards of various sorts.    If I was getting one of 
those new I would have got either a SAS or a Fiber channel interface for it (if 
it was available), as they tend to be less trouble than SCSI.

                                    Roger






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