Datlabs Technical Support Desk is often asked “what do you mean by a RAID?”
Well here is the answer: A RAID is a method of using a number of discrete hard disk drives or solid state drives in a data storage unit that presents users a more efficient and robust (less prone to downtime) means of access to their data. The term RAID is an acronym for Redundant Array of Independent Devices. An Array being a number of virtually interconnected hard drives , usually hard disk drives , with a practical upper limit determined by application, performance and capacity. There are a number of commonly used Array types but here we will discuss RAID 5 only. You can find technical detail concerning the popular RAID 5 configuration by clicking through to my RAID 5 data recovery page.
Do RAID 5 configured data storage systems fail?
A simple RAID 5 will tolerate a single hard disk drive failure, rebuild its data structures and continue to operate satisfactorily, however coincident disk failures will result in operational failure. Mathematically if a single independent element has a probability of failure of 1/10000 then two elements will have a dual probability of failure 1/100,000,000. However when a supplier creates an interdependent array of identical elements, the probability of a complete array failure will be median figure. Regardless of the mathematics concerning mean time between failures or MTBF, hard drive elements in a RAID Array have a shared environmental aspect that also contributes to a risk of failure. Power surge, power outage, data deletion, ransomware and malware attacks, rebuild errors, and poor maintenance practice, the list is long. Incorrect removal and replacement of hard drive elements is a common mistake that adversely affects the integrity of a RAID 5 configured system and the service it provides.
Is a RAID-5 server operation reliable?
In a RAID 5 configuration, data is striped across single hard disk drive elements and an error detection algorithm (single-parity) is used. RAID 5 reliability is dependent on all drives within the array operating correctly in order to fully auto rebuild in the event of a single point of failure. Despite the deployment of helium filled hard disk drives and other enterprise class construction technology, hard drives of a higher capacity are always more susceptible to increasing numbers of bad sectors, error rates and failure. “Putting all your apples in one basket is never a good idea”. You can find a good explanation of how RAID 5 is constructed here
RAID 5 configured server system failures
When a RAID 5 configured system fails, it is essential that it is gracefully powered down and no attempt is made to replace disks, or force a hard disk drive back online as this can result in incorrect data being written to the volume and cause irreparable data loss.
Here at Datlabs when we are tasked with a RAID 5 data recovery case we undertake the following procedures to militate against further data loss and produce the best possible data recovery outcome for our clients.
We create write protected duplicates of all healthy hard drives.
We create copies of the original hard drives using write-blocking technology that preserves the original data and we note the order in which the drives are configured in the array.
Rebuild and repair faulty hard disk drives and produce “as good as” copies.
The failed RAID 5 systems we receive generally have two or more faulty non working hard drives that have dropped out of the array and caused the failure of the system and the service it provides. The first task is therefore to undertake Hard Drive repairs and then attempt to make write protected copies that can be used to reconstruct and eventually rebuild of the system.
RAID 5 metadata determines which drive can be excluded from a rebuild.
Each hard drive in a RAID array has metadata that describes its function within the array. The metadata describes the last time that data was written to a given drive and this helps to determine which hard drive/s have exhibited as faulty. If two hard drives have failed we only need one of these failed drives data in order to facilitate a rebuild of the system and its data volume/s.
RAID 5 uses special parity functions to reconstruct any data on a single failed hard drive element however it cannot reconstruct its data if two hard drives have failed. After one hard drive fails, the rest of the array functions normally. But as time passes, the data on the furloughed hard drive becomes increasingly out-of-date. Sometimes, two or more hard drives fail almost instantaneously
We use the metadata to determine drive order, parity, rotation, stripe size.
The parity data created is written across all hard drives in the array. In order to reconstruct the failed array. Using the metadata on each drive, our RAID recovery team will determine how the data in the array has been distributed striped across the drives.
Emulate the physical RAID 5 array and find the logical units on the array.
Our RAID recovery technicians string the disk images together and then identify how the RAID 5 config storage has been logically allocated. They then locate the file system within the logical elements that will point to your stored data and facilitate an extraction.The file-system comprises a RAID system’s logical structure, acting as a road map to point you to the locations of your files.
We Run a scan on the RAID 5 array.
Logical corruption of a RAID 5 file system will affect the value of the recovery to our client. We scan the volume/s and detect any files that are orphaned as a result of a damaged or corrupt file system. Once complete we produce a file listing for our clients to check through and determine the usefulness of the available data.
We extract all available data from the failed RAID 5 array.
Our RAID Team will transfer all a clients data on to new external drives and return it to you