The bottle neck is the single scsi channel with daisy chained drives.
Scsi will drop down to the lowest level common speed between the drives
and the scsi card. LTO is a streaming technology and it uses speed match
to ensure it has a constant feed of data to write so that its doesn't
have to stop/start, rewind, etc. The lowest it can drop down to is 17
MB/sec. If data isn't pushed fast enough to it then it stops. Caches
data and starts. Because of buffers and caches (scsi card and tape
drives) it does appear to be stopping and restarting but it does.

If possible you should put your drives on separate channels. Try writing
data to only one tape drive, you'll get better performance. I push
terabytes of data to one tape drive and I have hit 80 MB/sec write
speed.

Do you have hardware compression enabled? 


Thanks,

Dana

-----Original Message-----
From: Legato NetWorker discussion [mailto:NETWORKER AT LISTSERV.TEMPLE DOT EDU]
On Behalf Of Librado Pamintuan
Sent: Wednesday, July 12, 2006 2:05 PM
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Subject: Re: Cloning from Disk

Our initial setup is backup to disk then automatically start cloning
after the savegroup is done, this creates a contention as you mentioned,
the disks are busy writing (from other backup sessions) while reading
the finished savesets to clone to tapes. So we stopped the automatic
cloning and instead created cron job to start it at 8:00 in the morning
to ensure that all backups were done. So just cloning from disk to tape
(no other activity on NetWorker) that's the throughput of 10 to 15 MB/s.
My tape drives are daisy chained and just using a single channel to
connect to the host/server using an LSI Logic 22320 HBA. I used
compression on my Unix clients at the client level and no compression on
WinNT/W2K and NetWare servers.


No issues on scsi, however I'm getting lots of this error on my
/var/log/messages file:
"connect failed or lost connection" on my iSCSI sessions.

>>> shawn.cox AT PCCA DOT COM 12/Jul/2006 11:47 am >>>

I do not believe that disk devices multiplex.  There is no need.

I can't tell from your message if you are cloning back to disk or to
tape.
If to disk then contention is probably your culprit as during the clone
you are reading and writing at the same time whereas during your backup
you are only writing to the disk device.  If you are cloning from disk
to tape, your pathways are completely different.  It may be that your
iSCSI and disk throughput are faster than your scsi pathway to the tape
device.

I have a similar setup to yours and typically see up to 60MB/sec writes
from many LAN clients to disk devices(mine are SAN attached not iSCSI).
But I cannot stage to my LTO2 tapes faster than about 30MB/sec which is
the limit for my SCSI connection to the tape devices.

Are your tape devices on a single scsi channel or separate channels for
each device?
Compression could be a factor, especially if you didn't use compressasm
at the client level.
You may have some scsi errors between the server and the tape devices
slowing down the throughput.
Anything else going on during the clone?

-Shawn

-----Original Message-----
From: Legato NetWorker discussion [mailto:NETWORKER AT LISTSERV.TEMPLE DOT EDU]
On Behalf Of Librado Pamintuan
Sent: Wednesday, July 12, 2006 12:10 PM
To: NETWORKER AT LISTSERV.TEMPLE DOT EDU
Subject: [Networker] Cloning from Disk

Good morning to all,
Just need to clarify and ask some question regarding cloning.
We are currently using an AX100i Storage Array for our disk backup with
12x
7.2 RPM SATA disk drives.

On backup process, I'm getting a descent throughput of 25 to 30 MB/s,
but when I start the cloning session, the throughput drops down to 10 to
15 MB/s.
Here's a possible explanation on the throughput issue, during backup,
data is written to disks at random while on cloning, Legato NetWorker is
de-multiplexing the savesets from the disk before it saves it to tapes,
thus reducing the throughput. Is this how is supposed to be? Is there
anyway to speed up cloning? or this any other faster method/process to
transfer the data from disk to tape?


Environment:
Server: PowerEdge 2850 dual 3.2 GHz processor with 4 GB RAM
O/S: Red Hat ES 3

NICs: 2 Intel PRO/1000 MT connected directly to tha AX100i storage array
Tape Library/Drive: ADIC Scalar 100 with 2 LTO-2 tape drives (scsi
connectivity).


thanks in advance,


Librado Pamintuan
Technical Support Analyst II
Information Systems Dep.
Operations Group
City of Regina


Phone:          (306) 777-7573
General Fax: (306) 777-6804
eFax:             (306) 546-6002
eMail:            lpamintuan AT regina DOT ca



<html><body><font face = "arial" size = "1">
DISCLAIMER: The information transmitted is intended only for the
addressee and may contain confidential, proprietary and/or privileged
material. Any unauthorized review, distribution or other use of or the
taking of any action in reliance upon this information is prohibited. If
you received this in error, please contact the sender and

delete or destroy this message and any copies.
</font><body></html>

To sign off this list, send email to listserv AT listserv.temple DOT edu and
type "signoff networker" in the body of the email. Please write to
networker-request AT listserv.temple DOT edu if you have any problems wit this
list. You can access the archives at
http://listserv.temple.edu/archives/networker.html or via RSS at
http://listserv.temple.edu/cgi-bin/wa?RSS&L=NETWORKER

To sign off this list, send email to listserv AT listserv.temple DOT edu and
type "signoff networker" in the body of the email. Please write to
networker-request AT listserv.temple DOT edu if you have any problems wit this
list. You can access the archives at
http://listserv.temple.edu/archives/networker.html or via RSS at
http://listserv.temple.edu/cgi-bin/wa?RSS&L=NETWORKER




<html><body><font face = "arial" size = "1">
DISCLAIMER: The information transmitted is intended only for the
addressee and may contain confidential, proprietary and/or privileged
material. Any unauthorized review, distribution or other use of or the
taking of any action in reliance upon this information is prohibited. If
you received this in error, please contact the sender and

delete or destroy this message and any copies.
</font><body></html>

To sign off this list, send email to listserv AT listserv.temple DOT edu and
type "signoff networker" in the body of the email. Please write to
networker-request AT listserv.temple DOT edu if you have any problems wit this
list. You can access the archives at
http://listserv.temple.edu/archives/networker.html or via RSS at
http://listserv.temple.edu/cgi-bin/wa?RSS&L=NETWORKER

To sign off this list, send email to listserv AT listserv.temple DOT edu and 
type "signoff networker" in the
body of the email. Please write to networker-request AT listserv.temple DOT edu 
if you have any problems
wit this list. You can access the archives at 
http://listserv.temple.edu/archives/networker.html or
via RSS at http://listserv.temple.edu/cgi-bin/wa?RSS&L=NETWORKER