Medical Imaging Data Storage: Hot, Warm, or Cold

Medical records retention includes keeping patient data on file. Proper medical records retention is advisable for successful long-term patient treatment. It is also valuable for legal and compliance issues, like medical malpractice suits, licensing board complaints, or audits. Several factors determine how many years medical records and imaging are to be stored and the type of storage selected.

As medical imaging becomes increasingly digital, image archives increase in size and require significant storage, that is scalable, resilient, easy to backup, and compliant with healthcare industry standards. When planning storage solutions for imaging archives, imaging data is often segmented into different tiers based on how often it needs to be accessed.
The three types of storage traditionally used for medical records and data are, hot, cold, and warm. Hot storage refers to fast, easy-to-access data storage like a local hard drive or quick-access cloud storage. Cold storage is for archival data that is rarely accessed and usually stored offsite. Cold storage is generally less expensive than hot storage, but can often take much longer to access. Warm data storage sits between the two, with the data stored close enough for easy access, but more cost-effective than hot storage data.
Data that is processed closest to its source will be the fastest. Data that has to travel over a few different networks to arrive on to Clinician’s screen can take longer to access. All data that is needed immediately must be placed in hot storage.

Comparison of different data storage types.

Hot Storage and Medical Imaging Data

Hot storage refers to frequently used and accessed data, such as documents on hard drives. This type of storage requires faster (and more expensive) hardware. Hot storage is for immediate and reliable access and includes data that is

  • Known to change
  • For clinician query purposes
  • Used in current projects
Machine Learning (ML) projects traditionally use hot storage as the data is read multiple times and needs to be provided to the ML model quickly.
Examples of hot storage solutions for medical images:
  1. Picture Archiving and Communication Systems (PACS): PACS are widely used systems for storing and accessing medical images. PACS typically use a combination of on-site servers and cloud-based storage to provide quick access to images from anywhere with an internet connection.
  2. Vendor Neutral Archives (VNAs): VNAs allow the integration of images from multiple sources, including different imaging modalities and vendors. VNAs typically use a combination of on-site and cloud-based storage to provide quick access to images.
  3. Cloud-based storage: Amazon S3, Microsoft Azure, and Google Cloud provide cost-effective and scalable solutions for storing medical images. These solutions typically offer high availability and can be easily integrated with other systems.
  4. Hybrid storage: Hybrid storage solutions combine on-site and cloud-based storage to balance performance and cost. These solutions typically use on-site storage for frequently accessed images and cloud-based storage for less frequently accessed images.
  5. Solid-state storage: Solid-state storage solutions, such as flash drives and SSDs, offer fast access times and are ideal for storing frequently accessed images. These solutions are often used with other storage solutions to provide a high-performance storage tier for hot data.

Cold Storage and Medical Imaging Data

Cold storage is used for data that is infrequently accessed or is used only for legal or regulatory compliance or archival purposes. Cold storage is often less expensive than other types of storage, but access to the data may be slower. It is the opposite of hot storage: this is data to keep, but rarely needs to be accessed. The rate of retrieving data and response time for cold storage data systems is slower than the services intended for managing active data. Cold storage is typically housed on a service such as Amazon Glacier, where it is ready to be accessed if required. The legal requirement for storing imaging studies varies by jurisdiction. In the U.S., many regions require providers to retain medical images for five to seven years, with certain cases requiring studies to be kept for over 20 years, such as in the case of minors. Cold storage is also appropriate for data that is no longer updated but is still queried. This data is also known as “dormant data.” Cold storage is similar to investing in a homeowner’s insurance policy in case of a disaster. In most cases, a healthcare organization won’t need to fully restore many files and may only need to retrieve a few if a disaster occurs. Most of the costs are associated with the retrieval of files, so keeping copies of images as an insurance policy becomes the economical choice.

Examples of cold storage for medical images:
  1. Tape storage is a cost-effective solution for storing large amounts of data, such as medical images. Tape storage is typically used for long-term retention and disaster recovery purposes, and images can be accessed relatively quickly using robotic tape libraries.
  2. Optical storage such as CDs or DVDs, can also be used for the long-term retention of medical images. However, this solution is becoming less common as tape and cloud-based storage solutions have become more cost-effective.
  3. Cloud-based storage is typically used for hot storage, although some cloud providers offer cold storage solutions that are specifically designed for the long-term retention of data, such as medical images. These solutions typically have lower retrieval times and higher costs compared to hot storage solutions.
  4. On-premises storage such as hard disk drives (HDDs) or network-attached storage (NAS), can also be used for cold storage of medical images. These solutions are typically less expensive than cloud-based solutions but require maintenance and may have limited scalability.
  5. Object-based storage such as Amazon S3 Glacier, is designed for the long-term retention of data and is typically used for cold storage. These solutions have lower retrieval times compared to tape-based solutions but are more expensive than on-premises solutions.

Cold Storage Tape Backups and the Cloud

While we mostly consider cloud-based storage when discussing imaging data, traditional storage still has a place in the industry. Traditional magnetic tape storage has been utilized since the 1950s and can still play a role in an organization’s backup plan. With a tape solution, large amounts of data can be stored reliably and cost-effectively. A tape drive provides sequential access storage, unlike a hard disk drive, which provides direct access storage. A disk drive can move to any position on the disk in a few milliseconds, but a tape drive must physically wind tape between reels to read any one particular piece of data. As a result, tape drives have large average access times. Tape archive refers to the practice of storing data on tapes, which are physical media used for long-term storage.

Tape backup is still in use today, although it has declined in popularity recently due to the proliferation of other storage technologies. Tape backup is often used for long-term storage, particularly for data that is not accessed frequently or is for regulatory compliance or archival purposes. In 2022, IBM introduced the Diamondback Tape Library, reaffirming that a magnetic tape is a relevant form of data storage. According to IBM, magnetic tape provides physically air-gapped isolation to increase resiliency against cyber security threats like ransomware. IBM’s latest tape storage solution targets organizations that require secure and scalable data storage for hundreds of petabytes, catering to both traditional data storage needs and the needs of “new wave” hyper scalers”—large global enterprises that handle enormous customer data sets.

Diamondback Tape Library. Source: IBM

While tape backup is not dead, it has become less common due to the adoption of cloud-based storage solutions. Tapes were popular in the past due to their relatively low cost and high storage capacity, but their physical fragility and degradation over time have made them less reliable for long-term storage. Tape backup can be used alongside cloud storage, such as cold storage, to provide a cost-effective and efficient storage solution. Cloud storage offers scalability, accessibility, and cost-effectiveness, particularly for cold storage. It is easily accessible from anywhere and more reliable than tapes as the data is stored on cloud provider servers.

Warm Storage and Medical Imaging Data

Data that requires continuous access without the restrictions forced by cold storage is fit for warm storage. Warm storage refers to data that is not actively being used but is still easily accessible. It is for data that does not need to be accessed as quickly as hot data, so it can be stored in a slightly slower, capacity-optimized environment. If you are concerned about overloading the hot storage, files can be stored in warm storage.

Here are a few examples of warm storage solutions for medical imaging data:
  1. Hard disk drives (HDDs) are a common storage solution for warm data in medical imaging. They deliver a good balance between cost and performance and can be easily integrated into existing infrastructure.
  2. Solid-state drives (SSDs) offer faster access times than HDDs, making them a good choice for warm data storage in medical imaging. However, they are more expensive than HDDs and may not provide as much storage capacity.
  3. Network-attached storage (NAS) is a scalable and cost-effective solution for warm data storage in medical imaging. NAS can be easily expanded as storage needs grow and can be accessed from multiple locations.
  4. Hybrid storage combines the benefits of both HDDs and SSDs, granting faster access times for frequently accessed data and lower-cost storage for less frequently accessed data.
  5. Cloud-based storage such as Amazon S3 Standard-Infrequent Access or Microsoft Azure Cool Blob Storage, can also be used for warm data storage in medical imaging. These solutions provide a balance between cost and performance and can be easily accessed from anywhere with an internet connection.
Examples of medical imaging data that could be stored in warm storage include medical images from routine check-ups or follow-up visits, as well as images that may be needed for research or audit purposes but are not accessed as frequently as hot storage data.

Determining Storage Type For Your Healthcare Organization

The best type of storage backup will depend on the specific needs and resources of the organization. Here are some factors to consider when deciding which type of backup is best
  1. Data access frequency: If fast access to data is needed, hot storage or warm storage may be the best option. If access data is needed infrequently, cold storage or tape archive may be more suitable.
  2. Data retention requirements: If data needs to be retained for a long time, tape archive or cold storage is the best option. These types of storage are more durable and less likely to suffer from data loss due to hardware failure or other issues.
  3. Budget: Cold storage and tape archive are typically less expensive than hot storage or warm storage, but access to the data may be slower. Consider your budget and the trade-offs between cost and access speed when deciding on the best type of storage.
  4. Data security: If data security is a major concern, consider using a cloud-based storage solution that offers encryption and other security features.
Ultimately, the best type of backup will depend on the specific needs and resources of the organization. It may be helpful to assess data storage requirements and consider the pros and cons of each type of storage before making a decision.
Want to learn more about VNA with the Dicom Systems Unifier platform? Meet with one of our enterprise imaging workflow experts.