« End of my internship | Home | Prize game – win a license for the Handy Backup Professional »
Guest post – Storage Virtualization
Do you still meet the data challenge by buying additional servers? Would you like to reduce costs and simplify data storage management? If the answer is yes to at least one of these questions – do read on.
According to the latest statistics, the volumes of data, used by the businesses are growing exponentially day by day. Historically, small and midsized organizations just bought new servers and used them until they needed new ones. Such an approach left its users with lots of unused space, high costs and low ease of storage management, etc. First for solving this problem company used NAS (network attached storage) servers, but now we are living in virtualization era. Storage virtualization provides its customers with efficiency to the storage environment, much better storage utilization, often reaching 80% or better, by using thin provisioning, easier storage management and more flexibility.
Storage virtualization: how does it work?
Storage virtualization abstracts logical storage from the physical one, helping to achieve location independence by abstracting the physical location of the data. The virtualization system presents a logical space for data storage and itself handles the process of mapping it to the actual physical location. There are three main implementation approaches :
- Host-based
- Storage device-based
- Network-based
Host-based virtualization requires usually specific device drivers supplemented by additional software. Physical disks presented to the host system, are handled by a traditional physical device driver. However, a software layer above the physical device driver intercepts the I/O requests performing the meta-data lookup and I/O redirection. It doesn’t need any additional hardware and have no infrastructure requirements, is really simple to design and code, supports any storage types and improves storage utilization without thin provisioning restrictions. The drawbacks of such an approach are as follows: storage utilization optimized only on a per host basis, replication and data migration are only possible locally to that host, software is unique to each operating system, and there is no easy way of keeping host instances in sync with other instances.
Solutions that use host-based virtualization are available from such vendors as Symantec VERITAS Storage Foundation, and FalconStor NSS Virtual Appliance for Vmware.
Storage device-based
Like host-based virtualization, several categories have existed for years and have only recently been classified as virtualization. Simple data storage devices, like single hard disk drives, do not provide any virtualization. But even the simplest disk arrays provide a logical to physical abstraction, as they use RAID schemes to join multiple disks in a single array (and possibly later divide the array it into smaller volumes).
Advanced disk arrays often feature cloning, snapshots and remote replication. Generally these devices do not provide the benefits of data migration or replication across heterogeneous storage, as each vendor tends to use their own proprietary protocols.
A primary storage controller provides the virtualization services and allows the direct attachment of other storage controllers. Depending on the implementation these may be from the same or different vendors.
The primary controller will provide the pooling and meta-data management services. It may also provide replication and migration services across those controllers which it is virtualizing. Pros of such an approach include: no additional hardware or infrastructure requirements, most of the benefits of storage virtualization, no latency to individual I/Os. As any approach it has its drawbacks: storage utilization is optimized only across the connected controllers, replication and data migration are only possible across the connected controllers and same vendors device for long distance support, downstream controller attachment limited to vendors support matrix.
Storage data-based solutions are available from few vendors: 3par Inc. and Hitachi Data Systems.
The third (and the most popular and cost-effective) approach is Network-based.
Devices (typically a standard server or smart switch) are connected via iSCSI of FC and form SANs (Storage Area Networks). These types of devices are the most commonly available and implemented form of virtualization.
The virtualization device sits in the SAN and provides the layer of abstraction between the hosts performing the I/O and the storage controllers providing the storage capacity. The list of pros really speaks in favor of such approach: true heterogeneous storage virtualization, caching of data (performance benefit) is possible when in-band, single management interface for all virtualized storage, replication services across heterogeneous devices, comparatively low cost.
Cons are as follows: complex interoperability matrices – limited by vendors support, difficult to implement fast meta-data updates in switched-based devices, out-of-band requires specific host based software, in-band may add latency to I/O, in-band the most complication to design and code.
Given the approach is really popular nowadays due to its pros, a large number of solutions are offered: StarWind Server and Enterprise Server by StarWind Software, DataCore Software SANsymphony&SANmelody, etc.
By Ilija Brajkovic | October 12, 2009
Tags: guest post, storage, storage virtualization, virtualization
Category: virtualization | Comments
Subscribe to RSS feed