Actually HP LTO3 drives (the best of any brand) can only slow down to 
27MB/s.

I know about num and size data buffers, and I have an admittedly
small DSSU on SATA disk (1.5T).  I'm pretty comfortable with my current
setup with DSSU for incrementals and some Fulls and only the jobs that I 
*know* are fast enough going directly to tape.  I have a Crossroads 10k 
which is a pretty nice FC-SCSI bridge for driving only four LTO2 drives, 
and can easily accomodate a pair of LTO3 drives in addition to its 
current load.  I have done the math to limit two LTO2 drives (max 
aggregate 120MB/s) to a single 2Gb FC connection (which should be able 
to handle 160MB/s).

I'm mainly curious how others have addressed that 27MB/s minimum.  I'm
concerned that my Sun/STK FLX210 (250GB and 400GB) SATA array may not be
fast enough.  At least one person has mentioned a FC DSSU which I find
quite interesting.  With LTO2 and LTO3 drives costing the same, it's 
getting harder to push back even if it does make the config more complex.

Does anyone have hard numbers?

Also, what about NDMP from a NetApp?  I have a 1.2TB filesystem on a 
NetApp with about 20 million files in it (my main reason for going to 
NDMP).  Will that FAS940 with 20million .jpg's be able to spin even an 
LTO2 (let alone LTO3) fast enough?  I understand that NDMP is closer to 
a ufsdump that a copy-one-file-at-a-time, but so far, the NetApp's 
scalability above 7.5 million files has not impressed me.

Is anyone sending NDMP backups to a DSSU?  Or is the NetApp fast enough? 
Are you able to measure it?

Thanks to Shyam Hazari for the throughput answer

bperror -all|grep "successfully read (duplicate)" |awk '{print $24}'

I never would have thought to read the error report looking for success :)

Write throughput can be scripted from this point.  The main trick is to 
distinguish between de-staging a DSSU and Vault.  Anyone?  I'm hoping it 
will be obivous tomorrow when I have some fresh Vault output.

Thanks for the great responses so far!


On Mon, 18 Sep 2006, Andrew Sydelko wrote:

> On Mon, 18 Sep 2006 11:58:38 -0500 (CDT)
> Joe Royer <jroyer at digitalmotorworks.com> wrote:
>
>> Forgive me if this has been asked before, I'm a bit behind on reading
>> the list.
>>
>> How do you keep your LTO3 drives spinning fast enough?
>>
>> I have a meeting with an idiot manager who refuses to believe that we
>> can't stream fast enough to use LTO3 without damaging the tape and/or
>> drive.  I have limited DSSU space.  I have been in environments in the
>> past where shoeshining was normal and so was the 20% failure rate and I
>> don't want to go back.  It is my understanding that most people aren't
>> spinning LTO3 fast enough and are living with higher failure rates.
>
> Keep in mind that LTO3 drives are able to stream at several different rates, 
> so even if you can't get the full bandwidth that the drive can write at, as 
> long as it's greater than 20MB/sec, you're not harming the drive.
>
>> The only thing I can think of is to send everything to DSSU first (TSM
>> anyone?), but NBU sucks at telling you the throughput there so I'm not
>> sure I trust that anyway.  Any tricks for getting throughput numbers out
>> of NetBackup (5.1) DSSU duplicates are very welcome.
>
> If you look at the "All Log Entries" report, you should be able to see the 
> bandwidth of your duplicates. These entries come from
> /usr/openv/netbackup/logs/bptm/log.<date> or 
> /usr/openv/netbackup/db/error/daily_messages.log.
>
>> My backup master with a 6-drive internal RAID-10 can barely hit 27MB/s
>> reliably doing OS backups, but my DSSU is on SATA SAN drives and hard
>> to measure.
>
> We've been very happy with the 3-ware controllers and SATA disks. Getting 
> more than 80MB/sec out of them at times.
>
> --andy.
>
> --------------
> Andrew Sydelko
> Engineering Computer Network
> Purdue University
>

-- 
Joe Royer / SysAdmin / Digital Motorworks / 512-692-1028


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