RAID 0 – Stripe
RAID 1 – Mirrors
RAID 4 and 5 – Stripes with dedicated or distributed parity
RAID 4 and RAID 5 volumes give you very high performance while still protecting your volume from disk failure. They are a great choice if you need high performance for writing large files or for reading files of any size. If you are using SSDs, RAID 4 is preferable to RAID 5; with SSDs, RAID 4 reads are up to 20% quicker, so it’s great for things like large video files that need to be read fast.
RAID 4 and RAID 5 are good for reading small files which are frequently read. They are not a good choice if you need to write a lot of small files as fast as possible. If you need to write many small files, we suggest you use RAID 1+0
How RAID 4 and RAID 5 volumes work.
RAID 4 and RAID 5 volumes are similar to stripe (RAID 0) volumes in that they spread the file data across all the disks used for a volume. However, RAID 4 and RAID 5 volumes generate and store parity information for data saved to them. This parity information can be used to recreate the data on a disk that has failed.
Parity information is created for each block of file data and written to the volume’s disks (see below for the way RAID 4 and RAID 5 do this differently). Parity information for a block of data is calculated by summing all the data on each disk for that block.
When a disk fails on a RAID 4 or RAID 5 volume, SoftRAID can take the file data from the remaining disks, along with the parity information, and regenerate the file data on the missing disk.
A simple example: imagine your volume contains 3 bytes of data – a, b and c – with values of 10, 20, and 30 respectively. The parity information for that byte will be the sum of those values, ie 60. The data is spread over the disks in the volume, so that a, b, c, and their parity information are never on the same disk. If the disk storing byte c fails, its value can be easily calculated by subtracting the combined values of bytes a and b from the parity information (which holds the sum of bytes a, b, and c).
What is the difference between RAID 4 and RAID 5?
The main difference between RAID 4 and RAID 5 volumes is how they store the parity information associated with the data on the disks.
RAID 4: The parity information for a RAID 4 volume is written to a dedicated disk called the “parity disk.” The other disks in a RAID 4 volume are called “data disks” as they store the file data for the volume. The parity disk is only ever read from if one of the data disks fails. This means that reading large files from RAID 4 volumes only uses the data disks.
Because only the data disks are read from, RAID 4 volumes can be up to 20% faster at reading than RAID 5 volumes, although this speed increase depends on the type of disk used and is most often seen with SSDs.
RAID 5: The parity information for a RAID 5 volume is distributed among all the disks of the volume. Each block of data, along with parity information for that block, can be written to anyone of the volume’s disks. So, unlike RAID 4 volumes, reading large files on a RAID 5 volume uses all the disks in that volume. Normally using more disks would make reading data faster, but with RAID 5 time is spent reading parity information which won’t be needed unless there’s a disk failure, thus reducing the speed of actual data read.
In all other respects (aside from how they deal with parity) RAID 4 and RAID 5 volumes are identical.
We recommend RAID 4 and RAID 5 volumes for…
We recommend RAID 4 and RAID 5 volumes for video editing, animation studios, digital photography, prepress and graphic arts. They are a great solution where you need the maximum amount of storage space, the highest performance, and protection against disk failure. With RAID 4 and RAID 5, the volume will keep working even after a disk gets an error or fails completely.
Creating the fastest possible RAID 4 or RAID 5 volume
Click here to find out how you can optimize your volume’s performance to achieve even faster read and write speeds.
RAID 1+0 (10) – Stripes with Mirrored Pairs
The Ultimate Combination of Speed and Data Safety
RAID 1+0 volumes are ideal for business customers who want the ultimate combination of speed and safety that this kind of volume provides. With SoftRAID, you can create RAID 1+0 volumes with up to 16 disks ie. 8 mirrored pairs.
How RAID 1+0 volumes work
RAID 1+0 volumes are made up of pairs of disks. Each pair, called a mirror pair, contains two disks that have identical information. If one disk in a mirror pair fails, the volume can keep reading and writing your files because it will use the other disk in the mirror pair instead.
The increased speed of RAID 1+0 volumes comes from striping mirrored pairs of disks together. Instead of striping together individual disks, like a stripe (RAID 0) volume, a RAID 1+0 volume treats each mirror pair just like a single disk of a stripe volume. RAID 1+0 volumes can only be made with even numbers of disks and require at least 4 disks.
Stripe Unit Size. In a RAID 1+0 volume, data is spread across the volume’s mirrored pairs of disks in blocks. The first block of the volume is on the first pair of mirrored disks, the second is on the second pair, etc. The size of each block is called the “stripe unit size.”
When you create a SoftRAID RAID 1+0 volume, you will be asked to select the stripe unit size for your new volume. SoftRAID will help you choose the correct value depending on the type of files you plan to store on your stripe volume.
Creating the fastest RAID 1+0 volume
Click here to find out how you can optimize your volume’s performance to achieve even faster read and write speeds.
Creating the most reliable RAID 1+0 volume
You can create a RAID 1+0 volume with disks in two enclosures. If the power supply, cables or disk interface in one enclosure fails, your RAID 1+0 volume will continue to work. A RAID 1+0 volume using two disk enclosures gives you the most protection from all types of hardware failure.
SoftRAID’s wonderful BLINK DISK LIGHT feature
The Blink Disk Light feature makes it super easy to create RAID 1+0 volume across two enclosures. In the SoftRAID application UI, disks are represented by tiles; when a tile is selected, the application will simultaneously blink a light, both on the tile, and the disk that is represented by the tile, making it really quick and easy to select which disks to use and find out which disks are in which enclosures. The blink disk light feature simplifies the complexity of creating a RAID 1+0 volume, making it easy to pick corresponding disks in two different enclosures for your RAID 1+0 mirrored pair(s).
We recommend RAID 1+0 volumes for…
We recommend RAID 1+0 volumes for any application where you want high performance and increased reliability. This is the RAID level we recommend for all our business customers.
Creating the fastest possible RAID volume
Using OWC ThunderBlades
With two OWC ThunderBlades striped together with SoftRAID XT, you can get lightning fast software RAID—faster than 3 GB/sec for reads and writes.
In fact, with OWC ThunderBlades, it’s now possible to get faster software RAID performance than is possible with a hardware RAID enclosure.
OWC ThunderBlades come bundled with SoftRAID XT, and you can choose from a range of SSD sizes from 1TB–4TB.
Optimizing all your SoftRAID volumes
The first 30-50% of a rotating disk is the fastest.
With rotating disk drives, the first (or outer) 30-50% of a disk is the fastest part – often 1.5 times the speed at the end of the disk. With SoftRAID, because you can use parts of a single disk for more than one RAID volume, you don’t have to use an entire disk to make a single RAID volume. In this way, a single disk can hold parts of different volumes of differing RAID levels (see diagram below).
For example, if you are creating a volume for video editing, we recommend that you use the only first 30 – 50% of each disk. Using just the first 30 – 50% of each disk in a RAID volume will give you a volume which has the highest possible performance for any file on the volume. You can then use the remaining space on each disk to create a different SoftRAID volume; perhaps a mirror volume where your data is secured against disk failure.
SoftRAID automatically chooses the fastest part of the disk for you
When you create a SoftRAID volume, the SoftRAID application automatically chooses the fastest part of the disk(s) available. If you have selected to use 40% of each disk for your first (and fastest) volume, SoftRAID will automatically create the volume using the first 40% of each disk.* Subsequent volumes will be made using slower parts of the disk(s). Because of this, make sure that you create the fastest volume first, and volumes where speed isn’t so important, after that.
*You can choose any percentage you like for each volume but for the best possible speed, make sure your first volume uses only the first 30-50% of each disk.
This ability to use a single disk for several volumes is an extremely powerful and flexible feature that is unique to SoftRAID.
Using two enclosures for safety and speed
Not only can your SoftRAID volume be spread over several disks but you can physically locate those disks in different enclosures. This increases safety (in the event of an enclosure failure) and—if you have a computer with 2 Thunderbolt chips, such as a 2013 Mac Pro—allows you to maximize connection speed.
GETTING MORE SPEED WITH 2013 MAC PRO
Although most Macs have 2 Thunderbolt ports, those 2 ports are controlled by only one chip inside. The 2013 Mac Pro has 3 chips controlling its 6 Thunderbolt ports; each pair of ports share the same chip (6 ports: 3 chips). With two ports that share a chip, the amount of data is limited by the bandwidth of that single chip, so plugging separate enclosures into those ports will not give you faster speeds.
With a 2013 Mac Pro’s three internal connector chips, you can double or triple the bandwidth; however, getting this extra speed is only possible if your enclosures are plugged into Thunderbolt ports connected to different chips. If your enclosures are plugged into ports that share the same chip, you won’t be achieving maximum transfer rates.
If you have created a volume that spans two enclosures, whose Thunderbolt cables are connected to different chips, you’ll be creating a volume which can achieve faster speeds than are possible with a single enclosure over a single Thunderbolt cable.
It’s like the difference between driving on a two-lane highway or a single lane road; you can get more vehicles through per minute if there are two lanes, just as you can get more data through (essentially making data transfer faster) using two Thunderbolt ports (connected to different chips).
Using two enclosures in this way is just not possible with hardware RAID.
Remember, even if your computer has only two Thunderbolt ports that share a single chip, you can still increase the security of your data by using two enclosures and a mirrored system (RAID 1 or RAID 1+0)
1. You can startup your Mac from a SoftRAID volume on any disk which supports booting. If a disk can startup your Mac when used with Apple’s Disk Utility program, it will work with SoftRAID. back
2. All disks fail at some rate. Good disks fail at a rate of about 3% a year, bad ones at 25% a year or more. Even SSDs (Solid State Disks) fail at about the same rate. After more than 500 hours of testing three popular disk brands, SoftRAID staff found – though most worked fine – one brand and model had a 33% failure rate. Your disk could be one that fails at a 3% rate, a 25% rate, or even higher; you won’t know till it happens. Even if you have one of the safer disks, over time, and with more disks, risk of failure increases to as much as 25%. Unless you use a RAID 0 volume as only a part of a larger backup system, your data is unprotected; if your disk fails, you could lose it all. back