SUMMARY: How to speed up LTO3 transfer ?

From: <>
Date: Wed Aug 09 2006 - 08:28:51 EDT
In general:

- after a few tests done with Casper Dik it turned out that ufsdump is the limiting factor; the array
  can do much, much more
- changing 'blocking factor' of ufsdump doesn't help
- LTO3 and the array are on two separated SCSI cards
- we can't change ufsdump to some other program

To sum up: we are stuck with the transfer..

Below is original question and all the answers.

----- Forwarded message from -----

> From:
> To:
> Subject: How to speed up LTO3 transfer ?
> Date: Tue, 8 Aug 2006 15:10:35 +0200
> Hello,
> we are doing backups of our v880 (Solaris 9) + array 3310 on LTO3 connected to LVD Ultra3 SCSI card.
> The SCSI card is put into 66MHz slot. What is strange is the transfer to the streamer:
> /usr/sbin/ufsdump 0uf /dev/rmt/1cn /dev/dsk/c3t0d0s0
> ...
>   DUMP: 91.76% done, finished in 0:35
>   DUMP: 93.98% done, finished in 0:25
>   DUMP: 95.45% done, finished in 0:19
>   DUMP: 97.09% done, finished in 0:12
>   DUMP: 99.41% done, finished in 0:02
>   DUMP: 1122170430 blocks (547934.78MB) on 1 volume at 21636 KB/sec
> Maximal, theoretical transfer rate is:
> uncompressed  80 MB/sec
>   compressed 160 MB/sec
> I don't expect we get the theoretical transfers but close to that. Our 20 MB/s
> is far from that. We have installed the latest patch for 'qus' and 'st/sd' drivers.
> Can you advice me what can we do to speed it up ?
> Regards
> przemol

Just guess that ufsdump is bottleneck ...
It may depend on a structure of data on ufs filesystem ...

I recommend you to increase block size.

from ufsdump(1M):
    b factor
          Blocking factor. Specify the blocking factor for  tape
          writes.  The  default is 20 blocks per write for tapes
          of density less  than  6250BPI  (bytes-per-inch).  The
          default  blocking  factor for tapes of density 6250BPI
          and greater is 64. The  default  blocking  factor  for
          cartridge  tapes (c option) is 126. The highest block-
          ing factor available with most  tape  drives  is  126.
          Note:  the  blocking  factor  is specified in terms of
          512-byte blocks, for compatibility with tar(1).

 question for you. The LVD Ultra3 SCSI card you have installed, is it a dual channel card (2 SCSI ports)? If so, is the
+3310 attached to one channel and the tape library attached to the other channel?

I would guess it is at least in part a limitation of ufsdump. You might
see different results with netbackup or legato networker driving the
tape backup. Also, how confident are you in your throughput to the 3310.
You might test doing a dump from one 3310 lun to another.

In my experience with LTO3's, unless you use a very large block size
(256K or larger), your performance will be in the 10-20MB/s range. Once
you use a large block size, the performance jumps to 80+ MB/s.

I dont know if ufsdump will allow a blocking factor of 512 or larger,
but that is what would be required.

1) backup local data to local data  (you already did)
2) alter block size of backup software. (in this case ufsdump )
3) increase number of streams that uses send to the backup job and do
multiplexing (this keeps the pipe full)
but for ufs dump, you cannot do multiplexing. (multiplexing is fast
for backup and slow for restore)
4) do disk to disk to tape backup. backing up many small files can
take longer time. If you tar all your files into one big file, this
may improve tape 'streaming'.

The question may be how fast the system can read from the array...what else
is going on while you are trying to backup?...and what is the max data
output of the 3310?

Other factors to consider are:
-number of files
-size of files - If there are lots of little files all over the disk, the
array is spending more time seeking then it is transferring data.

If you are transferring from the internal drives then 20Mb/s is about as much as you can expect from a V880.

When I worked on a system a couple of years ago, the fastest rate that the backup system could push out was 4MB.  So to fill+up the 23MB that our LTO2 could do, we had so stream 5 clients onto the same tape.  The data was interleaved which made
+restores slower.

I think ADIC has a new disk device that buffers the data before transfer to tape.  I don' t know if this is the right
+solution for you.

I have a similier issue, have you test the read performance of the disk
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Received on Wed Aug 9 08:29:39 2006

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