QuadStor VTL software

Using VTLs for primary backup storage is an easy way to speed up data protection and restore processes and also reduces tape handling complexity. In my opinion, VTLs are a must-have for all "traditional" backup operators that today still use physical tape as primary backup target. But VTLs have other advantages as well. Since they are based on standard Linux operating system they can provide CIFS and NFS network shares that can be used as backup to disk targets. Additionally, they implement most of the time data deduplication. This feature is especially perfect in backup environments where data is stored several times in identical data streams. Even with backup software that uses dedup inside (like Veeam) VTL-based dedup can even more reduce needed disk space.

All these advantages have a big disadvantage on the other side: it's called "price". VTLs are very expensive although they are based on standard hardware with standard storage systems. For example, a HP StoreOnce 4700 system (midrange VTL by HP) is based on a DL380 Gen8 server with two CPUs and plenty of RAM for the dedup work. For the storage HP uses D2600 diskenclosures with 12x2TB disks in RAID6 attached to a SmartArray controller. Inside the base unit there are two disks for OS. The OS is RedHat Enterprise Server with a locked down console to make some administrative work. So nothing special here but the list price is ~100.000$ with support. That's pretty much as the hardware costs are clearly below 20.000$. So what do you pay for?

It's the VTL emulation software and the dedup algorithm. Sure, they are pretty good and very stable and fast but are they worth the 80.000$?

So I was searching a bit around and found a small Indian company (QuadStor) that also offers a VTL software solution that provides nearly all the features of the StoreOnce, especially the dedup engine. That's the most important thing when using a VTL so if they can provide that too why not give them a try?

The software comes as RPM package for CentOS, SLES or Debian so you can use it on every commodity hardware you want to. Included are FC drivers to convert a standard QLogic FC HBA into a FC target, the dedup engine and a small but efficient webinterface. The software package is only 6MB in size.....

I've installed it onto a DL180G6 server with 2 Quadcore CPUs and 18GB of RAM. QuadStor recommends at least 8GB and doesn't make any recommendations about the CPU. You can use every block storage you want as backup storage so I created a RAID0 from 8 2TB SATA harddisks on the internal SmartArray controller. Booting up the OS, installing the software, starting the webinterface and voila... the VTL was ready to go.

First you need to create a pool. A pool is where you combine the block storage. In the pool definition you can enable or disable dedup and compression but that's all you need to do here.

From that pool you can create one or more tape libraries with one or more LTO drives. The QuadStor VTL can emulate Adic Scalar or HP MSL libraries with many drives and slots so you can configure nearly whatever you want.

Presenting the virtual tapes to a backup client is done on the command line since the webinterface has no option to do so. But even without Linux knowledge this is done quite easily and well documented (as long as you present the tapes to all servers the VTL can see but then you should have SAN based zoning in place)

Since the backup software sees the VTL as standard tape library nothing special has to be done here.

Starting withh the first backups I saw quite good performance. Backups were decently fast but CPU load on the VTL system was quite high. So it seems the VTL does highly depend on CPU cycles and cores. RAM usage was okay but this is normal within the first backup cycles. Only s fair amount of hash tables for the dedup engine has to be kept in RAM so memory capcity isn't a big problem at the beginning. But this will change very fast if you continue to put more load on the system. A lot more hash tables have to be kept in memory to prevent swapping them to disk what would render your VTL into a backup snail. That's why all commercial VTLs with dedup engine have that much RAM (192GB or more is usual).

You can see storage statistics like dedup ratio, compression ratio, used and free disk space, everything you need to know about your VTL storage subsystem.

So my backup and restore tests ran successfully and I began to wonder where is the rub. A free-of-charge software that apparently offers the same functionality as a high-price commercial system? I'm not finished with testing the system but by now I can say:

  1. dedup ratios aren't that high as you see them on commercial appliances. They are still very good and will save you plenty of storage
  2. backup and restore speed are fast within my test environment but I can't say if they really scale up to a "hundereds of TB" environment
  3. the recommendation of 8GB of RAM is really only for testing. As soon as you put more load on the system give the VTL as much RAM as you can afford (64GB should be the minimum)
  4. the same on CPU, don't use a old system with only 2 or 4 cores. 8-16 core should be the minimal way to go
  5. support: the support from QuadStor is free of charge during evaluation phase and can be converted to a paid support if you plan to use it in production. Costs are quite low with 2200$ for each VTL instance per year. Support can be requested by phone, mail or remote session and business hours are from 8am to 6pm GMT. I've contacted support a few times to help me sizing my VTL hardware and support responded fast and skilled. So for now thumbs up for the QuadStor support
  6. The software was stable and did exactly what it was designed for

To draw a bottom line: I think the software is really good. Perhaps not that good as the commercial products from vendors like HP or FTS but if you need a VTL and have a small budget, give QuadStor a try. Functionality is good, quality is good, support seems to be good and price is unrivaled.

For big installations I can't tell you currently but I think we will hear some more news from these guys and I hope they keep on going as they did in the last few months.

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