Data is the most valuable asset of any business today. Lost data means lost business! Even if you backup regularly, you need a fail-safe way to ensure that your data is protected and can be accessed without interruption in the event of an online disk failure. Adding RAID to your storage configurations is one of the most cost-effective ways to maintain both data protection and access.
While a number of companies offer RAID, not all RAID implementations are created equal. With over 24 years of SCSI development experience, only Thinkmate offers the most robust RAID data protection available today, based on a hardened RAID code proven over years of use in demanding environments and resold by most of the top-tier computer manufacturers.
To choose the RAID level that's right for you, begin by considering the factors below. Each one of these factors becomes a trade-off for another:
Adding RAID to your storage configurations is one of the most cost-effective ways to maintain both data protection and access.
RAID 1 usable capacity is 50% of the available drives in the RAID set.
RAID 1E usable capacity is 50% of the total available capacity of all disk drives in the RAID set.
Note: When using even numbers of disks it is always preferable to use RAID 10, which will allow multiple drive failures. With odd numbers of disks, however, RAID 1E supports only one drive failure.
RAID 5 has been the standard in server environments requiring fault toleranceRAID 5 uses data striping in a technique designed to provide fault-tolerant data storage, but doesn't require duplication of data like RAID 1 and RAID 1E. Data is striped across all of the drives in the array, but for each stripe through the array (one stripe unit from each disk) one stripe unit is reserved to hold parity data calculated from the other stripe units in the same stripe. Read performance is therefore very good, but there is a penalty for writes, since the parity data has to be recalculated and written along with the new data. To avoid a bottleneck, the parity data for consecutive stripes is interleaved with the data across all disks in the array.
RAID 5 has been the standard in server environments requiring fault tolerance. The RAID parity requires one disk drive per RAID set, so usable capacity will always be one disk drive les than the number of available disks in the configuration of available capacity - still better than RAID 1 which as only a 50% usable capacity.
RAID 5 requires a minimum of three disks to be implemented. RAID 5 usable capacity is between 67% - 94%, depending on the number of data drives in the RAID set.
RAID 5EE distributes the hot-spare drive space over the N+1 drives comprising the RAID-5 array plus standard hot-spare drive. This means that in normal operating mode the hot spare is an active participant in the array rather than spinning unused. In a normal RAID 5 array adding a hot-spare drive to RAID 5 array protects data by reducing the time spent in the critical rebuild state. This technique does not make maximum use of the hot-spare drive because it sits idle until a failure occurs. Often many years can elapse before the hot-spare drive is ever used. For small RAID 5 arrays in particular, having an extra disk to read from (four disks instead of three, as an example) can provide significantly better read performance.
For example, going from a 4-drive RAID 5 array with a hot spare to a 5-drive RAID 5EE array will increase performance by roughly 25%.
One downside of RAID 5EE is that the hot-spare drive cannot be shared across multiple physical arrays as with standard RAID 5 plus hot-spare. This RAID 5 technique is more costefficient for multiple arrays because it allows a single hot-spare drive to provide coverage for multiple physical arrays. This configuration reduces the cost of using a hot-spare drive, but the downside is the inability to handle separate drive failures within different arrays. This RAID level can sustain a single drive failure.
RAID 5EE useable capacity is between 50% - 88%, depending on the number of data drives in the RAID set. RAID 5EE requires a minimum of four disks to be implemented.
This RAID level is similar to RAID 5, but includes a second parity scheme that is distributed across different drives and therefore offers extremely high fault tolerance and drive failure tolerance. RAID 6 can withstand a double disk failure.
RAID 6 requires a minimum of four disks to be implemented. Usable capacity is always 2 less than the number of available disk drives in the RAID set.
Note: With less expensive, but less reliable SATA disk drives in a configuration that employs RAID 6, it is possible to achieve a higher level of availability than a Fibre Channel Array using RAID 5. This is because the second parity drive in the RAID 6 RAID set can withstand a second failure during a rebuild. In a RAID 5 set, the degraded state and/or the rebuilding time onto a hot spare is considered the window at which the RAID array is most vulnerable to data loss. During this time, if a second disk failure occurs, data is unrecoverable. With RAID 6 there are no windows of vulnerability as the second parity drive protects against this.
RAID 10 is the result of forming a RAID 0 array from two or more RAID 1 arrays. This RAID level provides fault tolerance - up to one disk of each sub-array may fail without causing loss of data.
Usable capacity of RAID 10 is 50% of available disk drives.
RAID 50 comprises RAID 0 striping across lower-level RAID 5 arrays. The benefits of RAID 5 are gained while the spanned RAID 0 allows the incorporation of many more disks into a single logical drive. Up to one drive in each sub-array may fail without loss of data. Also, rebuild times are substantially less then a single large RAID 5 array.
Usable capacity of RAID 50 is between 67% - 94%, depending on the number of data drives in the RAID set.
|Features||RAID 0||RAID 1||RAID 1E||RAID 5||RAID 5EE|
|Minimum # Drives||2||2||3||3||4|
|Data Protection||No Protection||Single-drive failure||Single-drive failure||Single-drive failure||Single-drive failure|
|Read Performance (degraded)||N/A||Medium||High||Low||Low|
|Write Performance (degraded)||N/A||High||High||Low||Low|
|Capacity Utilization||100%||50%||50%||67% - 94%||50% - 88%|
|Typical Applications||High End Workstations, data logging, real-time rendering, very transitory data||Operating System, transaction databases||Operating system, transaction databases||Data warehousing, web serving, archiving||Data warehousing, web serving, archiving|
|Features||RAID 6||RAID 10||RAID 50||RAID 60|
|Minimum # Drives||4||4||6||8|
|Data Protection||Two-drive failure||Up to one disk failure in each sub-array||Up to one disk failure in each sub-array||Up to two disk failures in each sub-array|
|Read Performance (degraded)||Low||High||Medium||Medium|
|Write Performance (degraded)||Low||High||Medium||Low|
|Capacity Utilization||50% - 88%||50%||67% - 94%||50% - 88%|
|Typical Applications||High End Workstations, data logging, real-time rendering, very transitory data||Fast databases, application servers||Large databases, file servers, application servers||Data archive, backup to disk, high availability solutions, servers with large capacity requirements|