RAID 0
Wed, 10/17/2007 - 08:48 — Tomas Hlatky
RAID 0
RAID 0 (Striped Set) implements striped disk array, the data is broken down into blocks (2 or more) without the information about check parity. RAID 0 is usually used to achieve better performance or it may be used for creation of little amount of big virtual disks. Resulting array is limited by smallest drive, e.g. if you use 160 GB disk and 100 GB disk, resulting array capacity is only 2*100 GB = 200 GB (and not 100 + 160 GB). Generally, the overall array can be described with equation SRAID0 = n × min (S1,S2, ...Sn), where SRAID0 is overall capacity, depending on number of drives, S1, S2 till Sn represent the size of each drive.
Best results are regarding write performance (theoretically n*, n = number of drives) and can be also achieved during reading of big files. It shouldn't be used during a work with big amount of little files, as overall performance may be degraded with longer access periods, as each time, disks have to search out for connected blocks on particular disks. Or to explain it better, if capacity of data, you are working with, is smaller than capacity of the stripe, there is no advantage of using of RAID 0 (Stripe = files are broken into stripes and distributed between the drives, on a picture on the left, you can see that block 1 and block 2 create one stripe, blocks 3-4 create another stripe etc.). Table describes the usage scenarios for permitted strip sizes.
Failure of any drive will result in loosing of all data in an array. Security level of your data is comparable with security of each drive, and is decreasing (indirect proportion) with number of units in the array: MTBFRAID0 ≈ MTBFdisk / n (MTBF = Mean Time Between Failures, also MTTF = Mean Time To Failure - mean time until expected critical failure, expected persistence, n = number of drives)
Table: Stripes size limits for correct integration of RAID.
That was the theoretical approach, now let's test the reality.
Intel(r) Matrix Storage Console
You can choose between two ways of RAID installation. When you press Ctrl+I, during POST, you will get the Intel(r) Matrix Storage Manager menu and there you can create desired RAID. Or you can choose more elegant way and create RAID directly from Windows in Intel(r) Matrix Storage Console. Second method is displayed in animation. In View menu important is to switch display of a console into Advanced Mode. Than choose Action fold in the Main Menu, and Create RAID Volume, you'll start up the Create RAID Volume Wizard.
2 x ST3500320NS & RAID 0
According to its description, Write-Back Cache only applies to RAID 5. The Volume Write-Back Cache is automatically enabled or disabled if an Uninterruptible Power Supply (UPS) is used. When a transition from AC to DC power occurs, as happens when the AC power source fails or is disconnected, the write back Cache will be flushed and disabled. When a transition from DC to AC power occurs, as happens when the AC power source is restored, the write back Cache will be re-enabled. While the Volume Write-Back Cache is enabled, multiple write requests can be combined. Writing the data from the Cache to the RAID 5 volume is more efficient. You can enable or disable this feature at any time without the need to restart the computer.
On the third screenshot, Burst Speed has enhanced from 2060,4 MB/s up to 2881,5 MB/s. This is due to the CPU frequency increase from 2133 MHz (8 x 266 MHz) up to 3200 MHz (8 x 400 MHz).
In the first column, ST3500320NS drive test results in AHCI mode are reported. In the second column, you can find reported results of two disks ST3500320NS set up in RAID 0, whereas W-BC was turned off. As I've already mentioned above, performance of two ST3500320NS in RAID 0 was twice as good in HDTachRW. However in application tests, performance increase was rather small. Though, after overclocking of CPU frequency up to 3,2 GHz and starting up the W-BC function, situation has changed. Sequential write has been much worse, but sequential read has slightly improved. There was marked change in Burst Speed, which has eightfolded. Looking at H2benchw results with W-BC on, it's clear that there is not any big difference between performance of single hard disk and two hard disks set up in RAID 0, there is only advantage of higher burst speed, which is, at the end, causing higher application index for 2 HDDs in RAID 0 with W-BC off. Situation is nearly identical in PCMark05. First place for best performance goes to combination of 2 HDDs set up in RAID 0 with W-BC off, second place, again thanks to high burst speed is for 2 HDDs set up in RAID 0 with W-BC on, and on the third place, there is single Barracuda ST3500320NS hard disk.
RAID 0 (Striped Set) implements striped disk array, the data is broken down into blocks (2 or more) without the information about check parity. RAID 0 is usually used to achieve better performance or it may be used for creation of little amount of big virtual disks. Resulting array is limited by smallest drive, e.g. if you use 160 GB disk and 100 GB disk, resulting array capacity is only 2*100 GB = 200 GB (and not 100 + 160 GB). Generally, the overall array can be described with equation SRAID0 = n × min (S1,S2, ...Sn), where SRAID0 is overall capacity, depending on number of drives, S1, S2 till Sn represent the size of each drive.
Best results are regarding write performance (theoretically n*, n = number of drives) and can be also achieved during reading of big files. It shouldn't be used during a work with big amount of little files, as overall performance may be degraded with longer access periods, as each time, disks have to search out for connected blocks on particular disks. Or to explain it better, if capacity of data, you are working with, is smaller than capacity of the stripe, there is no advantage of using of RAID 0 (Stripe = files are broken into stripes and distributed between the drives, on a picture on the left, you can see that block 1 and block 2 create one stripe, blocks 3-4 create another stripe etc.). Table describes the usage scenarios for permitted strip sizes.
Failure of any drive will result in loosing of all data in an array. Security level of your data is comparable with security of each drive, and is decreasing (indirect proportion) with number of units in the array: MTBFRAID0 ≈ MTBFdisk / n (MTBF = Mean Time Between Failures, also MTTF = Mean Time To Failure - mean time until expected critical failure, expected persistence, n = number of drives)
- Advantage: dramatically increased read and write transfer rates
- Disadvantage: no redundancy (if one hard drive fails, all data on the volume is lost)
- Applications: typically used in desktops and workstations to store high performance, non-critical data and software
Table: Stripes size limits for correct integration of RAID.
That was the theoretical approach, now let's test the reality.
Intel(r) Matrix Storage Console
Intel® Matrix Storage Console
You can choose between two ways of RAID installation. When you press Ctrl+I, during POST, you will get the Intel(r) Matrix Storage Manager menu and there you can create desired RAID. Or you can choose more elegant way and create RAID directly from Windows in Intel(r) Matrix Storage Console. Second method is displayed in animation. In View menu important is to switch display of a console into Advanced Mode. Than choose Action fold in the Main Menu, and Create RAID Volume, you'll start up the Create RAID Volume Wizard.
Create RAID Volume Wizard
Intel® Matrix Storage Console - RAID 0
2 x ST3500320NS & RAID 0
2 x ST3500320NS in RAID 0
2 x ST3500320NS in RAID 0 & Enabled Volume Write-Back Cache
2 x ST3500320NS in RAID 0 & Enabled Volume Write-Back Cache & CPU on 3.2GHz
On the first screenshot, you can see two ST3500320NS disks combined in RAID 0. Sequential write and read speed has doubled, as expected. Burst speed has enhanced from 226,4 MB/s up to nice 366,1 MB/s. Other two screenshots demonstrate much higher burst speed; Write-Back Cache (W-BC) method was used.According to its description, Write-Back Cache only applies to RAID 5. The Volume Write-Back Cache is automatically enabled or disabled if an Uninterruptible Power Supply (UPS) is used. When a transition from AC to DC power occurs, as happens when the AC power source fails or is disconnected, the write back Cache will be flushed and disabled. When a transition from DC to AC power occurs, as happens when the AC power source is restored, the write back Cache will be re-enabled. While the Volume Write-Back Cache is enabled, multiple write requests can be combined. Writing the data from the Cache to the RAID 5 volume is more efficient. You can enable or disable this feature at any time without the need to restart the computer.
Intel® Matrix Storage Console - Enable Volume Write-Back Cache
On the third screenshot, Burst Speed has enhanced from 2060,4 MB/s up to 2881,5 MB/s. This is due to the CPU frequency increase from 2133 MHz (8 x 266 MHz) up to 3200 MHz (8 x 400 MHz).
ST3500320NS vs. 2 x ST3500320NS in RAID 0
In the first column, ST3500320NS drive test results in AHCI mode are reported. In the second column, you can find reported results of two disks ST3500320NS set up in RAID 0, whereas W-BC was turned off. As I've already mentioned above, performance of two ST3500320NS in RAID 0 was twice as good in HDTachRW. However in application tests, performance increase was rather small. Though, after overclocking of CPU frequency up to 3,2 GHz and starting up the W-BC function, situation has changed. Sequential write has been much worse, but sequential read has slightly improved. There was marked change in Burst Speed, which has eightfolded. Looking at H2benchw results with W-BC on, it's clear that there is not any big difference between performance of single hard disk and two hard disks set up in RAID 0, there is only advantage of higher burst speed, which is, at the end, causing higher application index for 2 HDDs in RAID 0 with W-BC off. Situation is nearly identical in PCMark05. First place for best performance goes to combination of 2 HDDs set up in RAID 0 with W-BC off, second place, again thanks to high burst speed is for 2 HDDs set up in RAID 0 with W-BC on, and on the third place, there is single Barracuda ST3500320NS hard disk.
