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Power Loss Protection

Why In-Drive-UPS?

 Enterprise, industrial, embedded, avaition, aerospace storage system power supplies are designed according to the highest reliability standards. Designers are careful in selecting the most reliable regulation components. However, the reality is that power to data storage drives does occasionally fail.

 Since SSDs mentioned above maintain missioncritical data, it is unacceptable for previously stored data to be lost or for data in flight to nonvolatile storage to be corrupted.

 It is vital that these SSDs are designed to survive power reductions and outages without risk to the data itself.

 An effective power failure data protection mechanism needs to function before and after a disruptive power failure in order to provide comprehensive data protection.

 During a clean shutdown, most host systems initiate a command (The STANDBY IMMEDIATE Command) to an SSD to give it time to prepare for the shutdown. This allows the SSD to save data currently in transition (in temporary buffers), LBA mapping information, and/or Meta data to the non-volatile NAND media.

 In event of an unsafe power failure, the SSD abruptly loses power before the host system can initiate the STANDBY IMMEDIATE Command.

 Power loss events range from momentary loss of regulation (transient brownout condition) to loss of all power for an extended period of time. Such events can be caused by failure of the facility’s supply grid or UPS unit, failure of the system’s power supply (including fusing and cabling), failure of the SSD’s voltage regulation components, or mechanical failure of PCBs or connectors due to vibration, heat, or impact. Power failure risk at the SSD level depends only partly on the power delivery redundancy measures in place; power failure can cause system latency (when the drive needs to rebuild mapping tables) or permanent data loss.


Why SSD need In-Drive-UPS(Data Loss in Power Failure Scenarios)?

 When programming a NAND flash page, the program operation must complete to ensure the data is stored reliably within the page. Data is at risk if flash memory cells are in the process of being programmed when power to the drive is lost. The risk is compounded for MLC NAND flash memory, which uses the same physical page of memory cells to store two logical pages of data. When power is lost during program operation of the upper page, valid data already stored in the lower page cells can be damaged. This is typically referred to as lowerpage data corruption.

 Solid state drives have three areas of potential data loss or corruption when system power fails:


Loss of transit/temporary buffer data: This can occur due to the implementation of write caching (also called “write back” or “write behind”) to achieve peak performance. In this case, the host system is informed that a write operation has completed when in fact it is still in process. If power fails while the controller is “catching up” with the  write operation, the data in the write buffer is not yet hardened and can be lost. When the data is requested later by the host, the controller can either report the data irrecoverable or (depending on the controller design) it can deliver a previous “stale” version of those sectors to the host. In the latter case, this translates to silent data corruption, since the host system is not informed that the data delivered is incorrect.


Loss of mapping information/Meta data information: Every SSD controller uses mapping information to translate from the host’s logical LBA addresses to physical flash memory locations. Mapping information must be created and maintained if the data is to be later retrieved from the drive, and must be updated whenever new data is written to a previously written LBA. If the mapping information is lost when power fails, the drive may show data corruption, deliver stale (corrupted) data or may not be capable of supporting logical I/O on the next power up.

Lower page corruption: MLC or EMLC NAND flash uses each physical page to store the data of two logical pages; each memory cell represents two bits. The lower page (the logical page addressed by the lower of the two addresses) is programmed first, followed by the upper page. When programming the upper page, programming voltages are applied to the same cells already storing valid data in the lower page. If power fails while the upper page is being programmed, data in that page is lost, and alreadystored data in the lower page is corrupted as well. When that lower page data is requested later by the host, the SSD will report the data irrecoverable.

What kind of technology used by Comay SSD?

1. Avoid external DRAM cache

External DRAM cache can improve performance, endurance, etc. However, it is also a trouble-maker due to severe risk of data loss upon power loss.

CoreRise avoid external DRAM cache to eliminate such problems to ensure the safety of data and system.

2. High capacity supercapacitor

To enterprise SSD, industrial SSD/embedded SSD and some other SSD, the performance isimportant. However, the data safety is critical.

Comay SSD utilizes Supercap solution for some of these applications.

The power stored in Supercap is thousands more than general capacitors. It can supply 300~1000 ms for SSD to flush data to Nand.


3. Bank of discrete array of capacitors

In industrial, aerospace and military applications, the pursuit of performance is low, and the pursuit of reliability, especially environmental reliability and longevity, is high, and data is extremely critical.

For these applications, the Comay SSDs use a separate tantalum capacitor array to protect user data.

The tantalum capacitor used in the Comay SSD is one of the largest tantalum capacitors available. Still, the amount of power it can store is only one to one thousandth of a supercapacitor. For this reason, large-scale independent tantalum capacitor arrays and solutions without external buffers are critical.

The number of tantalum capacitors is usually in two digits depending on the reliability requirements of the solution and the capacitance of the tantalum capacitor used.

In addition, the energy that tantalum capacitors can store is related to their voltage and effective discharge voltage (usually squared). Therefore, Comay SSD usually use high voltage and high effective discharge voltage tantalum capacitors, which significantly improve the discharge performance of tantalum capacitors, ensuring data is foolproof.


Power failure protection FAQ

What is the meaning of the power-down protection function and the enhanced power-down protection function? What's the difference?

1、The meaning and difference between the power-down protection function and the enhanced power-down protection function

Whether it is a supercapacitor solution or a tantalum capacitor solution, the power-down protection function will lead to an increase in the complexity and cost of the SSD solid state drive.

Some manufacturers claim to have "enhanced power-down protection function" and "improved power-down protection function". What does this mean?

These are the commercial promotional actions that the vendor does after packaging some features. These statements are expressed in software to avoid losing data when power is lost, or a small amount of tantalum capacitors to provide regulation and backup.

In fact, whether it is software (firmware) method or a small amount of tantalum capacitor method, it can only reduce certain risks, and can not effectively prevent the risk of power failure, they can not claim to have "power failure protection" function.

Both the super capacitor solution and the tantalum capacitor solution have complex matching charging and discharging circuits and feedback mechanisms.

The so-called software power-down protection method is the master control of the SSD. When power is off, the data write request of the host side is no longer accepted. Data that is already in the cache is exposed to risk without protection

With a small amount of tantalum capacitors, the power-down protection function cannot be achieved.

Tantalum capacitors with high voltage, high capacitance and high effective discharge voltage should be used for 200~300ms, usually no less than 20. Only 2~4 capacitors can't achieve the same effect.

Overload protection

What is overload protection?

Generally, overload means current/voltage of circuit exceed the maxium rating for electronics devices. Overload protection is a safety mechanism intended to prevent or minimize damage that can occur from electrical malfunctions. Generally, if a problem occurs within an electrical circuit, the current of electricity will be automatically cut off by a protection system. 

Overload always heatsthe system, enlarges power consumption, even burns the devices.

As the key component, SSDs have to survive reliably upon overload events.


Why Overload protection is needed for SSDs?


1. More reliable, stable and faster

2. To be competent in harsh environments

3.Avoid direct and derived risks

Not only data and SSDs can be protected by Overload protection, but also computers,   devices, data center and other related equipments.


What consequences will be induced without overload protection?

1. System/Application/Service paralysed

2. Data loss

3. Host PCs,devices, datacenters burned


FAQ about Comay overload protection technology

Q1: Does Comay SSD use overload protection?

·           For now, all of Comay SSDs   employe overload protection technology.


Q2: Is Overload protection a complex or an advanced technology?

·           Overload is not a complex   technology, nor an advanced technology. It is because of the value of   CoreRise that CoreRise makes use of it firstly. As mentioned before, CoreRise   considers reliability as a priority, instead of cost all the time.


Q3: Is Overload protection a must for SSDs?

·           Yes, truely. Overload   protection makes SSDs more reliable, stable and avoids most risks.


Q4: Can overload protection avoid all kinds of power failure accidents?

·           Overload protection can survice   upon most kind of overload current or voltage. However, sometimes the SSD   would be damaged by overload if the abnormal current/voltage exceeded the   limit.

EECC Technology

EECC Technology

What is ECC technology? What is Enhanced ECC (EECC) technology?

ECC stands for “Error Correcting Code”. It is one kind of error correction and encryption-decryption algorithm. ECC technology can greatly improve the reliability of SSD. It the the prerequisite for Nand Flash to be used normally.

Meanwhile, the endurance is determined by ECC capability.


There are bad blocks when the Nand was produced. Afterwards, more bad blockswould occour. For the sake of reliability, bad block managment technology monitors and manages the bad blocks. However, mostly, there are only one or several bits of errors occur instead of whole page or block. ECC is supposed to fix such errors.

Generally, the strength of ECC is measured by max capability to fix errors. For instance, the ECC strength is 16 bit per 512B user data.

The EECC, is one kind of Enhanced ECC. The strength is doubled from general 16 bit/512B.


Why SSD need EEC?

1. EECC can greatly improve reliability

With the development of process of Nand Flash, the error rate is become higher.

It is indicated that UBER would decrease to only one tenth if the ECC capability doubled.

2. EECC can greatly extend endurance

The endurance is determined by ECC capability and EECC can greatly improve the endurance, finally the endurance of SSD.

As one of the most advanced technology, there is not a solid conclusion about the effect of EECC. Generally, it is believed that the endurance will increase 2-5 times.

With help EECC-like technologies, Anobit, LAMD claimed that they have greatly extend endurance.

Anobit annouced that they can prolong the lifespan of nand flash from 3,000 to 50,000.

FAQ about EECC

Value of EECC?

As above, EECC can greatly improve endurance, reliability of SSD at the price of trival cost increase.

Generally, UBER will become only one tenth and lifespan of SSD will increase by ten times if ECC capability doubled. EECC is the right key.


Can EECC eliminate the limit of Nand Flash endurance?

The effect of EECC is very amazing. However, there is no evidence that the limit can beeliminated.