Solid State Disk (SSD) - Frequently Asked Questions

The following list contains the most frequently asked questions about RamSan solid state disks and solid state storage technology:

Solid State Disk Systems and Technology
What is a solid state disk?
How much faster is solid state disk than a hard drive?
What is an IOPS?
What kind of memory do you use in your solid state disk?
Why should I purchase the RamSan instead of more memory for my server?
Will I lose data if I lose power?
Will I lose data if I lose a memory chip?
Will I lose data if a system has a catastrophic failure?
Can I monitor the RamSan with my SNMP monitoring software?

Unique Features of Flash Memory Technology
What is a cached flash RAID?
What is the difference between Flash memory and DDR RAM?
Can flash wear out?  Is there a write limit?
Can’t I just add flash drives to my existing storage array?

Solid State Disk Interoperability
Will solid state disk work with my operating system?
Will solid state disk work with my HBA, HCA, or Switch?
What HBA or HCA should I purchase to work with your solid state disk?
Can I attach the RamSan to my network attached system (NAS) filer?
Will the RamSan work with my file system?
Will the RamSan work with my server virtualization/clustering software?
Will the RamSan work with my multipathing software?
I don't have Fibre Channel or InfiniBand, can I attach your solid state disk?
Do I need a special driver or software to install your solid state disk?
Can I boot my operating system from solid state disk?
Do I need to modify my RDBMS software to work with the RamSan?

Using Solid State Disk Systems
How do I decide what data should be stored on solid state disk?
Do I need to store the entire database on solid state disk?
My database is several terabytes in size and your biggest solid state disk is 2TB how can this possibly help me?
What kind of applications are the RamSan used for?
Why would I buy your RamSan-400 when I can get so much more capacity with your RamSan-500?

About Texas Memory Systems
How long has Texas Memory Systems been in business?
What data is behind your World's Fastest Storage® trademark slogan?
Do you have any competitors?
What kind of support and warranties do you offer?
How much does a DDR RamSan cost?
How long after ordering will I get my solid state disk?
Do you provide evaluation units?
Do you offer a try and buy program or guarantee?
Can you help me determine if I need solid state disks?
Do you have any customers that I can speak to?
How do I buy a solid state disk?

Solid State Disk Systems and Technology

What is a solid state disk?

A solid state disk is a storage device that uses memory as the storage media. It is desirable to use memory as a storage media because it is much faster than traditional hard drives. Solid state disks look like a disk drive to the operating system; they can be mounted, formatted and used just like any other disk. Solid state disks come in many different form factors, Texas Memory Systems sells externally attached solid state disks that use Fibre Channel or InfiniBand to attach to servers or storage networks.

Solid state disks come in two primary types:  RAM-based and Flash-based.  As of Q4 2007 both types are available from Texas Memory Systems.

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How much faster is solid state disk than a hard drive?

Hard disk drive performance:

• 4-5 millisecond reads/writes.
• 150-300 random I/O’s per second.

DDR Solid State disk performance:

• 15 microsecond reads/writes.
• 400,000 random I/O’s per second.

Cached Flash Solid State disk performance:

• Cache performance:
  • 15 microseconds reads and writes.
  • 500,000 random I/O’s per second.
• Cache miss performance:
  • 200 microseconds reads (cache miss)
  • 2 milliseconds writes (cache miss)
  • 100,000 random I/O’s per second (reads)
  • 10,000 random I/O’s per second (writes)

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What is an IOPS?

An IOPS is an input/output per second. The number of IOPS a storage device can perform is always a factor of:

• The block size of the I/O (systems can do more IOPS with small block size transfers);
• Read versus write pattern (most systems do faster reads than writes); and
• Random versus sequential access patterns (most storage devices do much better with sequential data access instead of random data access ... solid state disks perform well with random or sequential accesses).

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What kind of memory do you use in your solid state disk?

RamSan-300 and RamSan-400 systems use 512 Mbit DDR RAM. The RamSan-500 system uses DDR Memory as cache and 16Gbit SLC NAND Flash memory as storage.

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Why should I purchase the RamSan instead of more memory for my server?

There are several reasons that a solid state disk might be a better solution than adding memory to a server. Here are some of those reasons:

• The RamSan is non-volatile. The memory in your server is volatile meaning that it loses data if you lose external power. The RamSan preserves your data even if external power is lost.
• The RamSan is external to the server. If your server reboots or crashes, you will lose all data in server memory. The RamSan is isolated from server instability and preserves data even if the server reboots.
• The RamSan can be shared across multiple servers. The memory in your server can only be used by that server. The memory in a solid state disk can be shared across multiple servers simultaneously.
• With DDR solid state disk, you never have a cache miss. In normal operating modes, your server memory is only used to cache recently read data and is worthless for really random data accesses to large data sets. With DDR solid state disk, you never have a cache miss because the data is permanently stored in memory.
• Solid state disks are a more economical way to accumulate large memory capacities. The higher the memory density in your server, the more you will have to pay for it. External solid state disks are not limited by processor to memory restrictions or even space constraints like servers.
• The RamSan does not need to be thrown out when you upgrade your server. New generations of servers almost always require new generations of memory. Even upgrading memory in a server might require upgrading to higher densities of memory. The RamSan does not need to be modified if you upgrade your server.
• RamSan solid state disks provide better memory protection than most server memory.

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Will I lose data if I lose power to a RamSan?

No. The RamSan-300 and RamSan-400 systems are equipped with redundant batteries and four internal hard disk drives. When external power is lost, the batteries will power the system under full operation for five minutes (this is just in case the power outage is temporary). After five minutes, the system will turn off Input/Output for the system and complete backing up all data that is in memory to the internal hard disk drives. Even if the system is fully loaded with memory, backing up to the internal disks will take no more than 12 minutes to back up. The batteries in the system are N+1 redundant, which means that there is enough battery capacity with just two of the three batteries to power the unit and complete backup after external power fails. The hard disk drives in the system are RAID protected which means that even if a hard disk drive fails, the other disk drives will be able to backup the system in the event of power outage.

No.  The RamSan-500 systems are equipped with redundant batteries to power the DDR cache long enough to flush the DDR cache to the Flash memory RAID.  Flash memory is inherently non-volatile and does not require power to save data.

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Will I lose data if I lose a memory chip?

No.  All new RamSan systems are shipping with Chipkill technology.  Chipkill protects your data even if an entire memory chip fails. Chipkill works in concert with the system's built-in ECC error correcting logic. If a memory chip fails, the system's ECC logic automatically corrects the resulting single bit errors thus preserving your data. IBM, one of the first companies to promote Chipkill, did a detailed study on the effect of Chipkill and suggests that it decreases the likelihood of data loss in a memory system by two orders of magnitude.

Additionally, the RamSan-500 has three levels of flash memory protection:  ECC, XOR, and RAID.  Each level isolates the user from single bit and multi-bit errors.  Our Flash SSDs have implemented RAID 5 across hot-swappable modules to protect against even an entire flash module failure.  In addition we have approx 20% more flash memory above and beyond the reported usable storage in the machine.  This is available as hot spares to replace any flash block or chip failures, as well to assist in wear leveling to increase the life of the write functionality of the flash.

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Will I lose data if a system has a catastrophic failure?

RamSan-300 and RamSan-400:

We have engineered a lot of redundancy into our RamSan systems. The systems have hot swap power supplies, hot swap and RAID protected backup hard disk drives, redundant batteries, redundant fans, ECC and Chipkill protected memory (essentially RAIDed memory), support for redundant controllers (with multipathing software), and a management controller that operates purely outside of the data path so that a failure does not stop data transfer. Even with all of these protections, it is still possible to have a catastrophic event that results in lost availability or data corruption. We believe the odds of this happening are similar to the odds of having two hard disk drives fail in one RAID group. For customers who require performance availability (i.e. you cannot lose performance or data if a system fails), we recommend mirroring units or arrays of units to each other. We have many customers at stock exchanges and financial trading environments where our mirrored systems provide constant availability. For customers who simply require data availability (i.e. you cannot lose access to your data but can handle a temporary drop in performance) then we can recommend some solutions that do not require mirrored solid state disk systems. Many of our customers use a single solid state disk and use their existing backup or database log replication strategies in the unlikely event of a catastrophic system problem.

RamSan-500:

We have engineered a lot of redundancy into our RamSan systems. The systems have hot swap power supplies, hot swap RAID protected flash modules, redundant batteries, redundant fans, ECC and Chipkill protected DDR cache (essentially RAIDed memory), and support for redundant controllers (with multipathing software). Even with all of these protections, it is still possible to have a catastrophic event that results in lost availability or data corruption. We believe the odds of this happening are similar to the odds of having two hard disk drives fail in one RAID group. For customers who require performance availability (i.e. you cannot lose performance or data if a system fails), we recommend mirroring units or arrays of units to each other.  For customers who simply require data availability (i.e. you cannot lose access to your data but can handle a temporary drop in performance) then we can recommend some solutions that do not require mirrored solid state disk systems. Many of our customers use a single solid state disk and use their existing backup or database log replication strategies in the unlikely event of a catastrophic system problem.

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Can I monitor the RamSan with my SNMP monitoring software?

Yes. The RamSan supports SNMP monitoring programs and provides a MIB for download. All items monitored in the RamSan are provided over SNMP.
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Unique Features of Flash Memory Technology

What is a Cached Flash RAID?

Cached Flash means a solid state disk with a large DDR RAM cache in front of Flash memory that is used as primary storage.  This lets a system leverage the benefits of flash: density, cost, non-volatility, and read performance and the benefits of DDR: blazing read or write performance.

What is the difference between Flash Memory and DDR RAM?

Flash and DDR are different memory technologies that store data in very different ways.  DDR memory is extremely fast Random Access Memory (RAM) that is used as the main memory in computers.  Flash is non-volatile EEPROM memory that is used in many battery powered consumer electronic devices.  The many characteristics of each are the following:

• DDR – Extremely fast to read or write, requires power to store data and backup systems for non-volatility.
• Flash – Fast for reads, reasonable speeds for writes, does not require power to keep data stored, low power consumption, and much more dense than DDR, requires wear leveling software to avoid wearing out the flash media.

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Can flash wear out?  Is there a write limit?

Yes.  However, the RamSan-500 is designed from the flash chip up to protect applications.  The system uses SLC NAND flash memory which has the longest write lifecycle of any flash memory chip with 100,000 writes per block, and each flash chip has over 16,000 blocks.  We use a DDR cache system to distribute the writes evenly over all the blocks in each flash chip, and across all the flash chips in the system.  We also have more flash memory in the system than what is reported as usable to spread the writes over more chips.  These functions are called wear leveling.  Our systems are designed so that even under the maximum write load it isn’t possible to wear out the flash in less than 3 years.  For example, the RamSan-500 holds 2 TB of usable storage, and can sustain a 2 GB/s write rate.  At 2 GB/s it takes 1024 seconds to write across the entire capacity.  To reach the write/erase limit this process would have to be done back to back 100,000 times, which would take 102,400,000 seconds.  Taking 102,400,000 second divided by 365 Days * 24 Hours/Day *60 Minutes/Hour * 60 Seconds/ Minute you get, 3.25 years.  This time is not taking the 20% additional chip storage or the large DDR cache into account to err on the conservative side.  If your workload writes slower than 2 GB/s than the flash will last much longer.  Most applications have small peaks of write IO and do not sustain anywhere near this write performance level.

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Can’t I just add flash drives to my existing storage array?

Most disk arrays have not certified Flash drives for their enclosures, so for most people the answer is no.  As manufactures begin to certify flash drives, they will need to re-architect their systems to leverage the performance of flash storage.  The current architecture is not well designed for high bandwidth or high IOPS from individual disks, and a significant latency penalty (~1 ms) is imposed by their front-end to cache.  This latency is significant because the controllers were designed with disks in mind.  With disks as the backend storage, imposing a 1 ms overhead on a 5-20 ms disk response time was trivial, however, this overhead dwarfs flash response time.  Additionally, buyers should be aware that there is a wide range between the performance and reliability of different flash hard disk drives.  The RamSan-500 is architected from the ground up with Flash in mind and has dramatically lower latency than other systems.
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Solid State Disk Interoperability

Will solid state disk work with my operating system?

Our solid state disks are tested with most open systems operating systems including: Windows, Linux (Red Hat, Suse), Solaris, HP-UX, AIX, IRIX, OpenVMS, HP Non-Stop, and Mac OS. For all of these environments, the RamSan is just another disk drive to the operating system.

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Will solid state disk work with my Host Bus Adapter, Host Channel Adapter, or Switch?

If a host bus adapter company (ATTO, Cambex, Emulex, LSI Logic, QLogic), host channel adapter company (Mellanox, QLogic), or server manufacturer makes an HBA or HCA to support open systems, then odds are we will work with it. If a switch company (Brocade, Cisco, Emulex, QLogic) makes a switch for open systems environments, then odds are that we will work with that switch also. Many of these companies are our customers or partners. They use our solid state disk to test performance of their own products.

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What host bus or host channel adapters should I purchase to work with your solid state disk?

Texas Memory Systems has started the FAST (Fast Access Storage Tested) program which is designed to recognize products that are certified interoperable and complementary to our RamSan line of storage products. The FAST-4 are 4Gbit Fibre Channel and 4x InfiniBand products that are critical to getting the most performance from the RamSan. These products have all been tested in the Texas Memory Systems interoperability lab. Please visit the FAST Program page for details.

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Can I attach the RamSan to my network attached system (NAS) filer?

Most network attached storage systems are now using Fibre Channel as the back end connectivity to storage. As such, the RamSan can attach to these filers as another storage device. The big question is whether your NAS vendor will support solid state disk attached to their filer. Today, OnStor and BlueArc have certified RamSan solid state disks with their filers. Other TMS customers have deployed the RamSan with other filer environments.

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Will the RamSan work with my file system?

Once you have connected the RamSan to your server, the LUNs presented by the RamSan can be formatted (or not) with any file system. In fact, since the RamSan can present up to 64 LUNs (1024 LUNs are possible with the RamSan-300 and RamSan-500), each of those LUNs could be formatted with a different file system. The RamSan is frequently used with SAN shared file systems such as Sun's QFS, Quantum’s StorNext, and Polyserve's Matrix Server.

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Will the RamSan work with my server virtualization/clustering software?

The RamSan has been tested and works well in most server virtualization (VMWare, Polyserve) and server clustering (Windows, Sun, IBM, OpenVMS, Oracle, etc) environments. The RamSan supports simple and persistent reservations. It is a SCSI-III compatible device.

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Will the RamSan work with my multipathing software?

Texas Memory Systems has tested and works with most multipathing software. TMS has developed an MPIO module for Windows 2003 environments. For Sun environments, we support MPxIO and Symantec's DMP. Where Symantec offers DMP, we support it. In IBM AIX environments, the RamSan works with RDAC, Cambex's multipathing software, and AIX's MPIO. In Linux environments, the system will work with built in multipathing tools. Where QLogic offers their built-in active:passive multipathing tools, we work with it. The RamSan does not work with EMC's PowerPath on any operating system other then Windows. On Windows our MPIO module is compatible with EMC's PowerPath version 4.6 and higher.

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I don't have Fibre Channel or InfiniBand, can I attach your solid state disk?

No. The time has come for you to leave the SCSI direct attached storage model. If you need the speed of solid state disk, you more than likely need the speed of 4Gbit Fibre Channel or InfiniBand. Both are as simple to install and connect as SCSI yet offer better performance, reliability and networkability.

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Do I need a special driver or software to install your solid state disk?

No. The RamSan works off of your operating system's built-in disk handling drivers and host bus or host channel adapter firmware.

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Can I boot my operating system from solid state disk?

In most cases, it is possible to boot your operating system from solid state disk depending on the operating system and the host bus or host channel adapter. If you can currently boot from SAN, then you can boot from the RamSan.

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Do I need to modify my RDBMS software to work with the RamSan?

No. Your database software does not care if data is stored on different storage systems just like it does not care if different files are in different volumes. It will adapt to the configuration without modification.

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Using Solid State Disk Systems

How do I decide what data should be stored on solid state disk?

You should store your frequently accessed data on solid state disk. Different customers take different approaches to this. In database environments, it is usually easy to identify the most frequently accessed tables or database components (by using tools such as Oracle's Statspack - see www.StatspackAnalyzer.com). Once the frequently accessed files are identified, they can be stored on the RamSan just like they are currently stored on another disk based system. Some customers get the most out of their solid state disks by constantly archiving off older data to slower RAID systems. Some customers only store database partitions with the last (days, weeks, months, years) worth of data. Some customers only move logs, indices, temporary tables, etc. In all cases, the goal is to only put frequently accessed data on solid state disk.  The large capacity of the RamSan-500 cached flash system will result in larger databases and parts of database stored on RamSan systems.

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Do I need to store the entire database on solid state disk?

No. Texas Memory Systems advises customers to only move their most frequently accessed files, tables, etc to solid state disk. For some customers, this means putting the entire database in solid state disk.

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My database is several terabytes in size and your biggest solid state disk is 2TB how can this possibly help me?

With the advent of the RamSan-500 system, accommodating large frequently accessed databases is becoming increasingly easy.  A single RamSan-500 system can provide 2TB of fast storage.  To scale to additional capacities, simply add more RamSan-500 units.  A standard rack can accommodate 20TB of RamSan-500 capacity.  For smaller databases or databases with write intensive components, the RamSan-300 and RamSan-400 are better choices.  For customers with large databases and heavy write activity across the database, our Tera-RamSan configuration, which is an array of our RamSan-400 systems, still offers the best price:performance on the market. 

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What kind of applications are the RamSan used for?

The RamSan is not limited to any specific applications. Historically the RamSan has been implemented to increase performance and system utilization in areas such as online transaction processing, data warehousing, file system metadata acceleration, database systems, non-linear video editing, software configuration and versioning tools acceleration and testing/benchmarking. Please see Solid State Disk Solutions for more ideas.

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Why would I buy your RamSan-400 when I can get so much more capacity with your RamSan-500?

The RamSan-400 will continue to be the system of choice for applications with sustained random writes or for smaller databases.  The RamSan-400 has approximately 1/10th the latency of the RamSan-500 (for cache misses).  The RamSan-500, however, is still more than 25x the speed of disks for reads and is ideal for read intensive purposes given its high density at an affordable cost.  The minimum entry capacity for the Flash system is 1 TB, so for customers with smaller data sizes the RamSan-400 is the best solution.  If an application requires the highest performance possible, our DDR systems are faster than our Flash systems.

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About Texas Memory Systems

How long has Texas Memory Systems been in business?

Texas Memory Systems was founded in 1978 and has been building solid state disk based systems over our entire history. The company is not venture backed and operates without debt making us a safer bet for your storage investment than the typical company.

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What data is behind your World's Fastest Storage® trademark slogan?

Texas Memory Systems customers regularly see profound performance improvements in their applications with RamSan products...as high as 2500%! To show an independent assessment of the RamSan's high performance, TMS joined the Storage Performance Council and publishes audited benchmark results from that body.

In published, audited and certified test results (audit identifier A00063) the RamSan-400 performed a record 291,202.58 SPC-1 IOPS ™ with .86 milliseconds latency. As a unified solution with other hardware and support options, it had a record low price/performance of $0.67 per SPC-1 IOPS ™.

But what does this mean? The SPC-1 benchmark is created to simulate intensive OLTP (online transaction processing) environments and the I/O intensive, random-style behavior typical in such environments. Compared to all other audited results, the RamSan-400 stands alone as a prime combination of performance and value.

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Do you have any competitors?

Yes. There are many manufacturers of solid state disks; however, our real competitors are the other methods IT managers use to try to solve I/O performance problems (buying new servers, adding processors, adding memory, buying cached RAID, adding spindles, and application tuning).

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What kind of support and warranties do you offer?

RamSan systems ship with a one year return to factory warranty but we can sell multiple year warranty programs including on-site support.

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How much does a DDR RamSan cost?

Our RamSan-300 systems start around £15,000 and increase from that point based on the system and the capacity. We like to talk to you about your application and help size your solid state disk requirement. You might not need as much solid state disk as you are thinking. According to the Storage Performance Council , the RamSan offers the best price to performance ratio of any tested storage device.

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How long after ordering will I get my solid state disk?

Our policy is to promise delivery within 30 days after order though we frequently are able to deliver systems before 30 days. The delivery time is long because we spend a lot of time burning in your system before it ever gets to you. Our solid state disks are burned in fully-loaded (memory and controllers) for at least three weeks. Once the unit is ordered, it spends at least two weeks being tested in the customer ordered configuration with commercial off the shelf host bus adapters or host channel adapters.

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Do you provide evaluation units?

Yes. Texas Memory Systems have a limited pool of evaluation units.

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Do you offer a try and buy program or guarantee?

Yes. Please see details of our "Application Performance Guaranteed" program.

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Can you help me determine if I need solid state disks?

We have developed a number of tools and methodologies to assist our customers and help determine if solid state disk is a good investment for your application. We will help you analyze operating system, database and application performance data to look for I/O bottlenecks. Please contact us at 0870 752 6250 for a free consultation.

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Do you have any customers that I can speak to?

Yes. Please read some of the TMS Solid State Disk Success Stories first. These customers have already invested a lot of their time in order to provide you with examples of how solid state disks benefits application performance. If you would like additional references, please contact us directly.

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How do I buy a solid state disk?

For more information on Solid State Disk or the RamSan product line contact the NAS sales team on 0870 752 6250 or complete and submit your contact details on the form provided under Contact Us