Thursday Mar 28, 2013

Is Tape Storage Still Harder to Manage Than Disk Storage?


-guest post by Brian Zents-

Historically, there has been a perception that tape is more difficult to manage than disk, but why is that? Fundamentally there are differences between disk and tape. Tape is a removable storage medium and disk is always powered on and spinning. With a removable storage one piece of tape media has the opportunity to interact with many tape drives, so when there is an error, customers historically wondered whether the drive or the media was at fault. With a disk system there is no removable media, if there is an error you know exactly which disk platter was at risk and you know what corrective action to take.

However, times have changed. With the release of Oracle’s StorageTek Tape Analytics (STA) you are no longer left wondering if the drive or the media is at risk, because this system does the analysis for you, leaving you with proactive recommendations and resulting corrective actions … just like disk.

For those unfamiliar with STA, it’s an intelligent monitoring application for Oracle tape libraries. Part of the purpose of STA is to allow users to make informed decisions about future tape storage investments based on current realities, but it also is used to monitor the health of your tape library environment. Its functionality can be utilized regardless of the drive and media types within the library, or whether the libraries are in an open system or mainframe environment.

STA utilizes a browser-based user interface that can display a variety of screens. To start understanding errors and whether there is a correlation between drive and media errors, you would click on the Drives screen to understand the health of drives in a library. Screens in STA display both tables and graphs that can be sorted or filtered.

In this screen ...

... it is clear that one specific drive has many more errors relative to the system average.

Next, you would click on the Media screen:

The Media screen helps you quickly identify problematic media. But how do you know if there’s a relationship between the two different types of errors? STA tracks library exchanges, which is convenient because each exchange involves just one drive and one piece of media. So, as shown below, you can easily filter the screen results to just focus in on exchanges involving the problematic drive.

You can sort the corresponding table based on whether the exchange was successful or not. You can then review the errors to see if there is a relationship between the problematic media and drive. You may also want to review the drive’s exchanges to see if media that’s having issues has any similarities to other media that’s having problems. For example, a purchased pack of media could all be having similar problems.

What if there doesn’t appear to be a relationship between media and drive errors? Part of the ingenuity of STA is that just about everything is linked, so root causes are easy to find. First, you can look at an individual drive to see its recent behavior, as show on this screen:

From the table you can see that this particular drive was healthy until recently. The drive indicated it needed a cleaning, and somebody performed that cleaning. However, just a few exchanges later, it started reporting errors. In this case, it’s clear that the drive has an issue that goes beyond the relationship with a specific piece of media and should be taken offline. On the other hand, if the issue appears to be related to the media itself, you should identify a method to transfer the data off of the media, and replace the media.

- Brian Zents

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Thursday Sep 15, 2011

How Content Management Makes Tape Drives More Efficient

Guest blog by Steve Aaker and Jamie Giovanetto

Oracle StorageTek's Enterprise Library Software (ELS) is the storage management software available for these Oracle StorageTek Tape Storage mainframe products:

In addition to its hardware enablement functions, ELS provides a rules-based content manager that can significantly increase the efficiency of your tape drives and systems. It's called the Library Content Manager or LCM for short, and it is described in the documentation for the ELS software.

For physical tapes, which can be native data or scratch cartridges, Multiple Volume Cartridges (MVCs), or cleaning cartridges and empty (free) storage cells, LCM places the tapes in the best location to:

  • Maximize the efficiency of the enabling software selections
  • Minimize the robotics activity at job mount time.

In the virtual tape environment, LCM controls whether a volume is in Oracle's StorageTek Virtual Storage Manager System buffer or only on an MVC at the appropriate time.

This content management capability can dramatically increase the efficiency of your tape storage.

An Example

Let's take the case where a StorageTek SL8500 modular library system from Oracle is totally full of cartridges and has no content management. All mounts and dismounts for the tapes in the library occur when required, but the question is whether that is sufficient. It is the minimum expected action, to be sure, but is it being accomplished in an efficient manner? If the cartridge to be mounted is in Library Storage Module (LSM) 03 and the drive where it is to be mounted is in LSM 00 (because that is the only location for that type of drive), the mount will take five major robotics actions. At dismount time, because there are no free cells, it will take another five major robotics actions to return the cartridge back to its source cell. In both directions, at least one of these robotic actions will be a move through the entire length of the library. When complete, the cartridge is back in LSM 03 and the drives it can be mounted on are still in LSM 00. Each time the volume is mounted, this scenario is repeated.

Now, let's look at what the same mount would look like in a content-managed StorageTek SL8500 modular library system. First, the cartridge to be mounted would have been placed in LSM 00 by a prior management run, which would have placed it in the LSM where the drives on which it could be mounted are located. Because of this management activity, the mount would require only two robotics actions, and the dismount would require the same. The reduction of three robotics actions, including that move through the entire length of the library, significantly reduces overall robotics time and results in much faster mount time. The cumulative mount times directly affect overall production time, so proper placement of volumes has a significant impact on production performance.

However, you might ask, "Didn't the cartridge have to be moved to the right place at some time? Didn't that take robotics activity?" Of course, it did. The difference is that content management activity would have been done outside the production job's execution time. In addition, the cartridge would have been placed where it can be mounted many times without requiring the many robotics actions required in the unmanaged example.

Note that this is just one of many examples where significant performance improvements can be obtained by active, rules-based content management. At its fullest implementation level, StorageTek LCM can bring scheduled production mounts down to sub-second levels in the virtual environment and, in some cases, to an average mount time that is approximately half the average mount time for an Oracle StorageTek SL8500 modular library system in the physical environment. Combined with its other capabilities and the underlying hardware and enabling software environment, Oracle's StorageTek Library Content Manager offers great enhancements to the automated tape environment.

- Steve Aaker and Jamie Giovanetto

Monday Feb 21, 2011

Red Tape, Part II


As I wrote last week, we recently announced the StorageTek T10000C Tape Drive, and along with it we released a number of related papers. I've been associated with publishing best practices papers for over a decade and it seems like there is no topic with less glamor for the writer – yet more importance for the reader – than the combined topics of backup/archive and restore/retrieve. The challenge has grown exponentially with the growth of disk storage. I remember the first time we sold a terabyte of storage: it was a room full of (big, heat-generating/power-consuming) 250 MB drives, costing millions of dollars. Now, just my home configuration consists of roughly 6 terabytes of disk.

How do you back up all of that storage? Tape: really fast tape. And, lots of it. This creates a whole variety of very interesting challenges today, elevating the topic to – at the very least – glamorous, but I think it qualifies as being downright hot! Fascinating areas include optimizing retrieving information from a vast achive of tape units, making sure that when you have backed up onto tape you can be sure it was done so without errors, and then there is the whole challenge of providing security. We have a paper for that!

Let's start off with the challenge of finding information on a serial, as opposed to random access, device. It can be done with brute force, and there are expensive solutions to assist, but the T10000C has a built in accelerator that relieves your system from the overhead. Learn how to use it by reading the concise Using Oracle's StorageTek Search Accelerator, by Oracle engineer Dwayne Edling.

Consider: you have invested big bucks to archive your priceless information onto potentially thousands of tapes. Of course, the latest tape drives all verify using ECC and CRC. However, these do not protect data that is being moved outside the storage device, resulting in a chance for data corruption as it is migrated across the storage landscape. The T10000C addresses this one step further by validating CRC check-sums generated at the host using Oracle's StorageTek Data Integrity Validation Solution (DIV). The brief article StorageTek Data Integrity Validation for the StorageTek T10000C Tape Drive, by the prolific Dwayne Edling, explains this problem in detail and presents some of the details of DIV.

Finally,we don't think twice about encrypting sensitive data on disks – what about on tape? One important aspect of enterprise security is the physical aspect: if someone stole the compact tape media, they could uncover all of your darkest secrets. The Oracle Key Manager (OKM) working with the Sun Crypto Accelerator 6000 provides a clean and highly efficient solution. You can read about this powerful combination in Oracle Key Manager Version 2.x Security and Authentication White Paper.

I have to be honest: I had never thought of Tape as a hot topic before. My bad!

- Kemer

Monday Feb 07, 2011

No Red Tape Here, Part I.

Old Tape DriveSome of us remember the good old days of computer tape. For example, I remember that the write protect ring on the back of the 6250 tape reels had a perfect balance: grasping the little tab and flinging it at the wall, the ring bounced back to be caught without leaving a mark on the lab. We did this as we waited for long compiles to finish and found other creative amusements with this simple component; I am old enough to escape retribution from my supervisors in making this admission, as they are long retired. But, I digress.

Tape as a backup medium – although in a much more sophisticated form – remains a staple of large enterprise backup. Last week we had a big announcement of Oracle's StorageTek T1000C Tape Drive, which offers 5 TB native uncompressed storage and a data transfer rated at nearly ¼ gigabyte per second. (To keep things in perspective, the 6250 stored 140 MB; I don't remember how slow it was, but it was well under 1 megabyte per second...) As a result of this announcement, we have released a number of technical papers that I thought I would discuss in a couple of blogs.

First of all, in thinking about speed, you won't want to miss Evaluating Tape Drive Performance White Paper, by Oracle engineer Dwayne Edling. Dwayne opens the paper by discussing the three components that limit tape speed:

  1. The speed that the storage application sends data to, or processes data from, the drive.
  2. The speed of the host interface between the drive and the application.
  3. The speed that the tape drive writes or reads data at the head/media interface.

6250 TapeHe then goes on to test the T1000C Tape Drive under a variety of conditions and comes to the important conclusion that in most situations, either the storage applications' speed or the drive throughput speed are the limiting factors in tape drive performance. Typical storage application throughput of 50-60 MB/s falls far short of the 400 MB/s maximum speed of a 4GB SCSI FCP interface. Even with compressed data, current tape drive technologies are also not able to write or read data any faster than a 4 GB (400 MB/s) SCSI FCP interface can push the data.

Back in the Jurassic age of computing, we naively assumed that tape storage was essentially "forever." That proved not to be the case! Another very interesting paper that addresses the issue of longtime archival is Protecting Your Archival Data With Improved Tape Dimensional Stability. This brief paper gives you some insight into the factors that make for longer lasting tape – its dimensional stability. Of course, some of these are environmental, but the substrate used is very important; advances in tape substrates have resulted in significant improvements over the last decade. Oracle's selection of aramid as the StorageTek T10000 T2 substrate has resulted in superior tape dimensional stability performance and long-term archival life.

Finally, don't miss Redefining Tape Usage With StorageTek Tape Tiering Accelerator and StorageTek In-Drive Reclaim Accelerator.The StorageTek In-drive Reclaim Accelerator and StorageTek Tape Tiering Accelerator, an important innovation in the T1000C Tape Drive, provide the capability to randomly access, add or delete physical partitions. This paper goes into the nitty gritty of how this works.

Existing tape media can store more than a terabyte of user data. In the near future, a single tape media will hold tens of terabytes, with 100 TB capacities in the foreseeable future. Managing these multi-terabyte tape cartridges requires a new approach for managing data on tape. Oracle has developed a new tape storage format with the StorageTek T10000C tape drive, using an innovative partitioning architecture, that allows the addition or removal of storage space as needed. With these capacities and efficiencies, tape remains an important medium for enterprise archiving.

- Kemer


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