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Backup is taking more time using LTO4 in HP MSL 8096

cdslmum
Advisor

Backup is taking more time using LTO4 in HP MSL 8096

I am taking a raw volume backup of my server data size is 2.2 TB in HP MSL 8096 using LTO 4 it is taking 4.45-hrs in NATIVE mode.But this is the same time taken by LTO-3 tape previously.To make the backup quick we have changed LTO-3 to LTO-4 but the is no improvement.Kindly suggest me any changes to be done.

Thanks in advance

Badhusha
4 REPLIES
VK2COT
Honored Contributor

Re: Backup is taking more time using LTO4 in HP MSL 8096

Hello,

Your information is incomplete but let's try to help:

a) Did you install Library and Tape Tools to
check your setup?

b) What is the version of your HP-UX server?

c) What is the model of the LTO-4 tape
drive:

Ultrium 1760
Ultrium 1840

d) From memory, MSL 8096 with four LTO-4 1840 drives offers maximum sustained transfer rate (with 2:1 compression rate)
of around 3.4 TB/hour. That would mean
roughly around 0.85 TB/hour for a single
drive.

e) What is the software that copies
raw database to tape?

Cheers,

VK2COT
VK2COT - Dusan Baljevic
Bill Hassell
Honored Contributor

Re: Backup is taking more time using LTO4 in HP MSL 8096

LTO-4 tape drives are extremely fast and will not run at full speed until the data is presented slightly faster than the data rate of the drive. If you use the compressed device file, the data rate coming from the disk must be at least twice as fast as the tape drive. Here are the LTO minimum data rates:

LTO1 = 15 MB/sec
LTO2 = 30 MB/sec
LTO3 = 60 MB/sec
LTO4 = 120 MB/sec
(LTO5 is faster but I'm having trouble locating the MB/sec so I'll guess at about 240 MB/sec)

So your LTO3 is performing quite well (or more accurately, your disk is sending data fast enough to keep the tape drive from slowing down). Starting with LTO3, a feature called Data Rate Matching was introduced to help with slow disks. DDS, DLT and older LTO drives cannot slow down -- they have only one speed. If the data doesn't come fast enough, the tape drive must halt, reverse direction, then pause to wait for more data to arrive. If the disk data rate is slightly less than than the tape drive, then these repositioning sequences can reduce throughput to 20%, even as bad as 5% of normal speed. Repositioning has an enormous effect on throughput and as you might expect, it wears the tape and the tape drive unnecessarily.

The fact that LTO4 seems to run at the same speed as LTO3 indicates that the disk simply isn't fast enough. For filesystem backup, high performance backup products will read 5 or 10 separate files at the same time to create a data stream fast enough for these modern tape drives. But a raw volume backup means a single data stream from the disk and multiple reader processes can't improve the data rate.

Now the backup software should be a high performance product designed for very high throughput. Improving the disk throughput requires analyzing all points along the data chain. For a JBOD disk, there is probably little you can do -- these tape drives exceed the sustained read rate of most disks. For a disk array, increasing the cache size won't help during backup as all the data being read will be new to the cache after a short time. Striping the disk LUNs will help immensely.

The interface speed (array to computer) should be a minimum of 2 Gbit and if a SAN fabric is in the middle, end-to-end performance of the fabric will be a concern. Then the computer interface should be maximized with multiple paths. This would have to be coordinated with the array capabilities and will require a path manager like PowerPath or HP-UX multi-pathing. Finally, a slow computer will prevent full speed.



Bill Hassell, sysadmin
cdslmum
Advisor

Re: Backup is taking more time using LTO4 in HP MSL 8096

My HP-UX ver is
# HP-UX cdsdrs B.11.23 U 9000/800 3450146013 unlimited-user license.

Media = HP LTO 4 ULTRIUM RW 1.6 TB C7974A

Backup S/W :- HP Software Dataprotector 6.0

Server is connected to library and EMC2 DMX4 storage with FC card(2GB).
I am not able to confirm 1760/1840

Regds
Badhusha
Marino Meloni_1
Honored Contributor

Re: Backup is taking more time using LTO4 in HP MSL 8096

Most of the time the limitation is not due to the target but to the source.
Are you sure you can read the data fast enought to feed the LTO?
you may use LTT and run the system performance test in order to identify is the cause of the bandwidht limitation is due to the source of the data