Transfer Rates for LTO tapes, should I be concerned?

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Transfer Rates for LTO tapes, should I be concerned?

Veeam Logoby pawel » Mon Jan 12, 2015 6:23 pm

I am looking at taking a large chunk of my budget this year and setting it aside for tape storage. We have a regulatory requirement that all our data must be stored for 7 years at minimum. I want to use Veeam B&R Enterprise+ to replicate off-site daily. In addition to meet to regulatory requirements I want to backup 30 days of data to shared storage (I have that working well so far) and at the end of the 30 days offload the backups to tape before they get purged.

I am looking at an HP LTO-6 drive with LTO-5 media. My data at the end of the 30 days will be about 1TB and will likely grow to 2.5TB in the next 2-3 years (which is why I want to buy an LTO-6 drive upfront).

When talking to some folks that have far more experience with tapes than I do a point was brought up that Veeam will have to send data to the tape at a rate of 110MB/s (when compressed) to avoid buffer underrun conditions. To be honest this is the first time I heard of this. What worries me is that currently I can only transfer data from the ESXi host at about 50-60MB/s, backup copy jobs from NAS storage using iSCSI are faster at 70-150MB/s. This was more than fast enough for my application but clearly it won't satisfy the native 110MB/s transfer rate of the tape drive.

How does Veeam handle this? Or do I need to look at a way to make the backup copies run much faster?
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Re: Transfer Rates for LTO tapes, should I be concerned?

Veeam Logoby Dima P. » Mon Jan 12, 2015 10:57 pm

Hi pawel,
Quick question from me comes first – are you going to attach you tape library directly to NAS (which as I understood is you main long term repository)?
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Re: Transfer Rates for LTO tapes, should I be concerned?

Veeam Logoby pawel » Mon Jan 12, 2015 11:02 pm

I was planning on attaching it directly to the server where Veeam is installed, which is a physical MS Server 2012. The NAS is where all my backups are targeted to and where they are stored. So Veeam will have to get the backups from the NAS using iSCSI and load them to an external tape drive which will be directly connected to it.

Thanks!
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Re: Transfer Rates for LTO tapes, should I be concerned?

Veeam Logoby dweide » Tue Jan 13, 2015 7:44 am 1 person likes this post

pawel wrote: will have to send data to the tape at a rate of 110MB/s ...... to avoid buffer underrun conditions


From my understanding that statement is true to achieve optimum performance and to reduce wear on the LTO drive.
If you dont reach that data rate the drive will have to stop when the buffer is empty and restart when new data is available in the buffer. And that start/stop operation ads stress to the drive and is not recommended in terms of drive lifetime.
But its not like in the dark ages when a buffer underrun would ruin a CD beeing burnt, its just not optimal.

I have been using a HP LTO5 librarry with a different backup software (HP DataProtector) for the past 5 years and was hardly ever able to reach the native data rate of the drive due to bottlenecks in my source storages. I never experienced any problems, the backuo was simply slower than theoretically possible.
The same is true after moving to a HP LTO6 library last year.

And in addition the newer drives are said to be able to dynamically reduce the write speed, I recommend to double check that with your hardware supplier.
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Re: Transfer Rates for LTO tapes, should I be concerned?

Veeam Logoby Dima P. » Tue Jan 13, 2015 4:19 pm

Agree with dweide. Goggling gives me the following info on tape drive generations: Ultrium 6 ranges from 40 to 160 MB/sec and 40 to 140 MB/sec on Ultrium 5. So, since 5th generation there is a built in Digital speed matching functionality which corrects the exact writing speed of the drive in case of the infrastructure bottleneck
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Re: Transfer Rates for LTO tapes, should I be concerned?

Veeam Logoby pawel » Wed Jan 14, 2015 5:23 pm

Great, thank you to the both of you. The exact drive is Ultrium 6250, I'll do some more digging to check if it can dynamically reduce the write speed. I'll also update once I have everything up and running to see how it works.

Thanks!
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Re: Transfer Rates for LTO tapes, should I be concerned?

Veeam Logoby seadave » Wed Jan 14, 2015 10:58 pm

If you are using a NAS as your backup target, you will be constrained by 1Gbps which theoretically tops out at 125MB/s, in reality closer to 90-100MB/s with network overhead (unless you have really slow drives and odd RAID set on the NAS which could be slower). The type of switch you are using to connect the two devices also needs to be of decent quality unless they are direct connected NIC to NIC. If you have the NAS mounted as a volume against your server, you might want to test with IOMeter or HD Tune Pro to see what your max throughput is.

We purchased a spanking new 730XD with 16 x 4TB SATA drives. We constructed a RAID using the H730P PERC card that comes with that system. I settled on RAID6 with one hot spare to maximize reliable data. I realize I get some write penalties, but after testing with HD Tune Pro, I was getting anywhere from 150MB/s to 900MB/s depending on the block size used for testing.

We proceeded to use this configuration to backup our VMs. The SAS is Equallogic and the Veeam server communicates with the hosts over 1Gbps Ethernet. As to be expected, our job throughput tops out at ~130MB/s with the contention being identified as the source and never the target (Veeam RAID 6 array).

This worked great until we tried to swing over our Dell TL2000 tape library with a LTO4HH drive. We always used that library with an iSCSI to SAS bridge over 1Gbps Ethernet. Unfortunately the throughput is capped at 50MB/s according to Dell and was confirmed in our onsite tests. We are backing up WAY more data with Veeam then we did previously, so after much fussing and learning about PERC RAID vs HBA when it comes to tape libraries, we purchased a Dell 6Gbps HBA card (~$200). Was a bit of a pain to clear out the iSCSI config and tape drivers, but after finally doing so (and making sure to use the "install non-exclusive" driver provided by Dell), we are now getting ~110MB/s to the tape. It is incredible how much faster it is at processing jobs. Seems to be more than just 2X.
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