Disk Spanning (ディスクスパニング)

複数のドライブを一つとして扱い、合計容量はボリュームの一番小さいドライブでの倍数となります。スパニングはRAIDではなく、アレー(Array)です、

データ記録時、内蔵しているドライブの順番に書き込みます。データ記録の高速性や復旧機能がありません。

2 hard drives Spanning 2HDD
4 hard drives Spanning 4HDD

Disk Striping  (RAID 0, 別称: ストライピング)

複数のドライブを一つとして扱い、合計容量はボリュームの一番小さいドライブでの倍数となります。データ記録時、パソコンからデータを受け取って、内蔵している各ドライブに分散して書き込んで保存されます、データの転送スピードは速くなります。但し、ドライブ故障時、データの復旧やアクセスは不可となります。

2 hard drives RAID0 2HDD
4 hard drives RAID0 4HDD

Disk Mirroring (RAID 1, 別称: ミラーリング)

内蔵している複数のドライブは2台ごとで1ペアとして扱い、ペア毎の容量は2台 ドライブの合計容量の50%とになります。

データ記録時、ペアにはそれぞれ同じデータが記録して保存されます。万が一、ドライブ故障時に新品を交換して、ペアのドライブからデータの復旧ができます。

 

2 hard drives RAID1 2HDD

Disk Mirroring with Striping  (RAID 10, ミラーリング&ストライピング)

ドライブ2台でデータを2重化したペアを、さらに2台×2でまとめて1ペアのHDD(アレイ)としてデータを分散して保存します。各ペアには、それぞれ同じデータが記録されます。

万一のドライブ故障時には、ドライブを交換し、ペアのドライブからデータを復旧できます。同じデータを保存したペアのドライブが同時に故障しない限り、最大2台までのHDD

の故障に対応できます。

4 hard drives RAID10 4HDD

Disk Striping with dedicated parity (RAID 3, ストライピング&専用的パリティー)

データ記録時、内蔵している4台ドライブ内の3台にデータを分散して高速で書き込みます。同時に、データからパリティー(誤り訂正符号)を生成し、4つ目ドライブに保存されます。万が一、3台のドライブのうち、どれか1つドライブが故障しても、ドライブ交換することで4つ目ドライブの保存されるパリティー内の情報から復旧が可能なモードです。

ドライブ4台は3台分の容量が使用できます。

3 hard drives RAID3 3HDD
4 hard drives RAID3 4HDD
3 hard drives
1 hot spare disk
RAID3 3+1HDD

Disk Striping with distributed parity (RAID 5, ストライピング&分散的パリティー)

データ記録時、内蔵している4台ドライブにデータを分散して高速で書き込みます。同時に、データからパリティー(誤り訂正符号)を生成し、データとともに複数のドライブに分散して記録します。万が一、4台のドライブのうち、どれか1つドライブが故障しても、ドライブ交換することでパリティー内の情報から復旧が可能なモードです(HDD4台で構成時)。

ドライブ4台は3台分の容量が使用できます。

3 hard drives RAID5 3HDD
4 hard drives RAID5 4HDD
3 hard drives
1 hot spare disk
RAID5 3+1HDD

ご注意

  • ご利用のドライブは同じ容量のを使用してくださるようお勧めします。

 

RAID 5A redundant array of independent disks (RAID) can be used to improve the I/O performance and therefore offer faster transfer rates, mirror the data for redundancy in case of a disk failure or combine the storage capacity of multiple disks to create one large volume. Depending on the RAID controller and the amount of drives, different RAID modes can be used.

AKiTiO's data storage products make use of both hardware and software RAID, depending the model. A hardware RAID is created by a built-in RAID controller and is independent of the computer and the operating system. A software RAID is created either by the operating system of the computer or by the software that is running on the product itself (e.g. MyCloud series).

In both cases, it's important to consult the user documentation before setting up the RAID, as each product and RAID controller works slightly different.

 

Important

Important information about AKiTiO's hardware and software RAID

Software vs hardware RAID

Hardware RAID - The RAID is created and managed by the RAID controller inside the data storage product. The RAID is independent of the computer and the operating system. This means that you can move the drive from one computer to the other and assuming that the file system (e.g. NTFS or HFS+) is recognized by the operating system, you will always be able to access your data.

Software RAID - There are two types of software RAID. For network drives like the MyCloud series, the RAID is created by the embedded Linux system. For direct attached storage drives without RAID controller like the AKiTiO Thunder2 Quad and the AKiTiO Thunder2 Quad Mini, the RAID can be created by the operating system on the computer (e.g. Mac OS X or Windows 8). The RAID is dependent on the operating system and the data cannot be accessed from another system.

Preventing data loss

Just because a product supports RAID doesn't mean the data is automatically safe. Even when using a RAID mode with redundancy (e.g. RAID 1 or RAID 5), it’s always best to keep a second copy of your data in a different location. This could mean that you keep the original data on your computer or make a second backup somewhere else. Doing so makes it possible to easily and quickly recover your data even if you accidentally delete files, the data on that drive gets corrupted, the RAID controller fails or something else happens to your hardware and hard drives (e.g. natural disaster or computer virus).

Preparing enough storage space may be expensive up front when you need to buy additional drives but if your data is valuable, it is well worth the investment. If you currently don't have another backup location and there is not enough space to keep the original data on your computer, consider buying a second RAID enclosure and another set of drives at the same time. Buying the same RAID enclosure for the second backup unit has the additional benefit that it can act as a backup for the hardware too (e.g. same RAID controller, same power supply).

Protecting existing data during setup

If you have some existing data on the drives that you intend to use in a new RAID, make sure to backup the data in a different location first. When you setup a new RAID or change the RAID mode, all existing data is lost! The exception to the rule is Non-RAID but even then, it's better to have a backup than lose data in case something goes wrong during the setup.

Recovering and accessing data on a RAID array

For hardware RAID, the data can only be accessed when the drives are installed in the original product where the RAID was originally created. It's not possible to move the drives to another product without re-formatting the drives. The exception to this rule is when both products are based on the same RAID controller and the same firmware version. However, even then, it's important to make sure that the settings are identical and it's best to create a backup of all the data in a different location first, before moving the drives.

For software RAID, the data can be accessed on other computers that are running the same operating system (e.g. MacBook Pro and MacBook Air both with OS X 10.9) but it's not possible to access the data from a completely different system (e.g. Windows and Mac OS). For network drives like the MyCloud series, the disks should be installed inside a product that is based on the same firmware and the drives will have to be mounted manually.

Expanding the storage capacity for an existing RAID

Whenever you change something on an existing RAID, be that installing larger drives or adding additional drives, it's necessary to create a new RAID system.

  1. Backup all the data from the old drives in a different location.
  2. Replace or add the new drive(s).
  3. Set your preferred RAID mode and format the drives.
  4. Move all the data from the backup location back to the newly created RAID.

RAID modes

Depending on the RAID controller and the amount of drives, you can select between different RAID modes to setup the disks according to your own requirements.

  • RAID 0 - Disk striping is used where speed is the primary objective.
  • RAID 1 - Disk mirroring is used for redundancy in case of single disk failure.
  • RAID 5 - Disk striping with parity is a good compromise for performance, redundancy and storage capacity.
  • RAID 10 - Disk mirroring with striping is used for redundancy in case of a single disk failure.

Some additional terms that are used for AKiTiO's products include Non-RAID, JBOD, SPAN and BIG. The exact definition of these terms depends on each model but following is a general description.

  • Non-RAID - No RAID is created and the disks can be accessed seperately. They are presented to the system as independent logical volumes. This mode is sometimes also known as JBOD.
  • BIG/SPAN - In most cases these terms mean that the disks are combined into one single volume for maximum storage capacity. In some AKiTiO products, this mode might also be labelled as JBOD.

 

Disclaimer:
Information in this article is subject to change without notice. AKiTiO does not make any representations or warranties (implied or otherwise) regarding the accuracy and completeness of this document and shall in no event be liable for any loss of profit or any other commercial damage, including but not limited to special, incidental, consequential, or other damages. All brand names and product names used in this document are trademarks, or registered trademarks of their respective holders.