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Raid backup server in depth

  • 4
    Oct

Raid backup server in depth

RAID is the short form of Redundant Array of Independent Disks. RAID refers to the way of combining different independent and small disks into single storage of large size. The disks which constitute this array are called the array members. In order to get upgraded speed and performance, several physical disks are integrated as one set. Different levels of RAID types: RAID 0, RAID 1, RAID 5, RAID 6 and RAID 10.

Different levels of RAID processing

RAID 0
It is the initial level of the process. In a RAID 0 system data is written to disks in the array as different blocks. Performance can be enhanced by using several disks at once. There are different controllers, one controller per disk, which is used to increase performance. RAID 0 can be used to combine two drives storage into a single volume. RAID 0 is supported on Linux, OS X, and Windows. The benefit of RAID 0 is that one disk failure does not affect the data of the second disk.

RAID 1
In this data is stored in two drives one is data reader and the other one is a mirror drive. In case of failure of one drive the other drive is used for data recovery and operated. We need a minimum of 2 drives for RAID 1 array.

RAID 0+1

This is based on the combination of RAID 0 and RAID 1. This level inherits RAID 0 performance and RAID 1 fault tolerance.

RAID 1E

This can survive failure of 1 member disk or many numbers of non-adjacent disks. It uses both striping and mirroring techniques to store data in an array. There are 3 subtypes of the 1E layout.

  • RAID 1E near: This can be created using only an odd number of disks. If the number of disks is even, then this turns to RAID 10.
  • RAID 1E interleaved: This can be implemented either by odd or even number of disks. It is created by a controller like IBM.
  • RAID 1E far: This can be created by using any number of disks. This is similar to RAID 10. In order to recover such RAID, you should use a host protected area (HPA) to cut the half number of member disks and then recover RAID 0. This is because it is not possible to automatically recover configuration for RAID 1E far.

RAID 5
It is the regular level of RAID process. In RAID 5 we need minimum 3 disks which can work for 16 blocks. The disks are divided into data blocks and every disk has an equal part of the data block written. The data is dispersed over all drives of raid backup server instead of writing on a single drive. The computer can determine the data from another block of the set in case of data unavailability. Which means that RAID 5 array supports single disk failure without any data loss. In RAID 5 a hardware controller is suggested even it is identified in software. To increase the performance of writing, the extra cache can be used.

RAID 5E

This is one of the RAID 5 variations. In additional to RAID 5, RAID 5E have integrated share space to rebuild the array in case of one member disks fails. The advantage of RAID 5E compared to RAID 5 is high read and write space with the dedicated drive. However, this leads to the complexity of rebuild during member disk failure. This can be created by using a standalone controller like the IBM ServeRAID controller.

Recovery of array parameters in RAID 5E is similar to RAID 5.

RAID 6
RAID 6 is equal to RAID 5 but the same data is written on two disks. This means to support 2 disks we need 4 disks. If the 2 disks are lost another 2 can be used. Unlike the RAID 5 in RAID 6, the array can survive on the second failure. In RAID 5 one disk fails, replacing with a new one takes time, during this if another disk fails data may be lost forever.

RAID 10
The benefits of RAID 0 and RAID 1 can be grouped to a single system. The mirroring of all data on secondary disks while using each disk set can speed up data transfers and also provides security.
Several mirrors are created where the data is arranged in tapes on multiple disks, later extracted disk sets are mirrored. RAID 10 level has fault tolerance which is equal to RAID 1 with advancing read or write speeds on a single RAID 1 volume. In this RAID 10 level, 4 disks are needed.

RAID overview
For any business, data is the key resource. Data loss may result in business loss. Keep the regular back up to save some effort to access or to protect in case of drive failures. Using raid backup server along with storage configurations can be an economical way to secure and access the data.

 Characteristics of RAID

  • It is fault tolerant. This means even if one of the disks fails, it does not fail as a raid storage system. As there are multiple disks, the mean time between failure (MTBF) increases. As data is stored in a redundant manner, recovery becomes possible.
  • Performance is much better compared to a single disk. The read and write speed of the array shows significant improvement.
  • The capacity of RAID is defined as the amount of user data that is written into the raid storage devices. This must not be always equal to the individual disk capacity of each of the disks.
  • RAID gives a way to store similar data in various locations on many physical raid storage devices. That is why it is called ‘Redundant’.

RAID storage techniques

Following are the main techniques of storing data in a raid storage system:

  • Striping: In this method, the data flow is fragmented into blocks of a certain size called block size. These blocks are then written across RAID one by one. This way of data storage increases performance. This makes RAID a good option in video editing systems.
  • Mirroring: This is a storage technique where multiple copies of the same data are stored in different RAID members. Raid backup server improves fault tolerance as well as performance.
  • Parity: In this technique, a certain parity function is calculated for data blocks. In case of a drive failure, the missing block is recalculated from the checksum which in turn improves fault tolerance.

All the existing RAID types are based on either of these three techniques and also a combination of the above.

RAID Implementations

RAID can be created in the following ways:

Software RAID

This is the most inexpensive solution. This method uses operating system drivers. Most of the operating systems have an in-built capability to create many RAID levels. For example, the Windows operating system allows the user to create RAID 0, RAID 1 and RAID 5. However, it is inseparably linked with the Windows operating system and so its partitions cannot be used like in dual boot.

Software RAID is created based on the user computer and so this uses host CPU for implementation. In case of RAID 0 and 1, the load on the CPU is negligible whereas, in case of RAID types that are based on parity, 1 to 5 percent of CPU load is used depending on the number of disks. However, for practical purposes this is negligible.

It must be remembered that there are some limitations to boot the system if software RAID is used. Only RAID 1 support boot partition, and it is impossible to system boot with software RAID 0 and 5. In most cases, software RAID does not implement hot swapping and so is not suitable where continuous availability is required.

 Hardware RAID

Hardware RAID is formed by using separate hardware. This can be done in one of the following ways:

  • RAID chip is built into the motherboard which is pretty inexpensive.
  • A more expensive option is using a standalone complex RAID controller. These controllers are supported with their own CPU and battery build up cache memory.

Advantages of Hardware RAID over Software RAID

  • As it does not allow host computer, so CPU performance is not affected.
  • This allows the user to create boot partitions, unlike Software partition.
  • Error handling is improved, as communication with devices is direct.
  • It supports hot swapping.

RAID 5 Recovery

The manual process to recover RAID 5 is too complex and time-consuming if you are not an expert. Using ReclaiMe Free Raid Recovery you can recover drive much easily.

  • Download ReclaiMe Free Raid Recovery
  • Using the Disks button, create and open disk image file of RAID 5 member disks.
  • Select the available member disks and start RAID 5. You should at least two of the disks. RAID 5 works even if one disk is missing.
  • The RAID recovery finishes when Scan is done.
  • After the RAID 5 configuration parameters are restored, you should select one of the following:
  • Run ReclaiMe data recovery software to recover data. This will launch in RAID recovery mode and display the partition on the raid backup server.
  • You can save the recovered array parameters in a file in XML format. Also, you can open this file in ReclaiMe and start recovering data.
  • You can also transfer the recovered parameters to some other data recovery tool you might want to use.

If you want to recover data manually, you have to determine the parity position and rotation to get the full configuration of your array. This is because like RAID 0, RAID 5 is a redundant array and stores parity data.

RAID 0 Recovery

RAID 0 can fail due to any of the following reasons:

  • Failure of one or more RAID 0 member disks.
  • Failure not associated with disk failure.

 

 Member disk failure

As RAID 0 arrays are non-redundant, so if one of the disks on the raid storage system fails, data is lost forever. However, you can try to recover data from other member disks. Only the files having a size smaller than (N-1) *(block size) can be recovered. If the file was stored on the failed disk, data cannot be recovered even if the file size is less than the above-mentioned threshold.

Other issues

Various other factors can also lead to RAID 0 failures. For example, operator error, controller error or RAID 0 controlling software. In these cases, the configuration metadata is lost, but member disks are working fine.  With these failures, it is possible to recover data from RAID 0. Firstly, you determine the raid backup server configuration.

  • A number of member disks present.
  • The order of the disks, which array was present in the first position.
  • Block size
  • Starting offset for the disks.

You can either opt for manual or software process for RAID 0 recovery. The software process is similar to the RAID 5 recovery process using the software described above.

For manual recovery, you need to determine raid storage devices order manually. You can use log files with a timestamp for this purpose. Also, you need a disk viewer tool. Whenever a fragment of the suitable file is found on one of the member disks, this tool tracks which disk contains the next fragment and so on.

To determine the first disk, you can again use the disk viewer tool. Search the member disks for:

  • The disk which contains the MBR in case of hardware RAID is the first disk.
  • The disk which contains the boot sector at the beginning is the first disk in case of software RAID.

For a hardware RAID 0, the block size can be determined by looking up possible values or checking in the manual which block can be used in your RAID 0 implementation. For software RAID 0, The standard value can be used. For example, Windows use 128 sector block for RAID 0.

On a hardware RAID 0, data mostly starts at the start of the hard drive. This is equivalent to setting start offset of member disk to 0. For a software RAID, the offsets are mostly identical.  This can be identified by locating the volume sector.

Hot Swapping hard drive when RAID crashes

If there is no raid backup server downtime when RAID crashes and you need to change the raid backup drives, then below is the process to swap hard drive when RAID crashes.

RAID 5 disk mirroring provides highly secure data protection in the event of failure. To create a RAID 5 array, you need 3 disks of similar capacity. RAID creates an exact copy on each of the raid backup drives and protects data in case of any of the drive failure. The usable capacity in RAID 5 is the disk size of the smallest drive. This is useful for personal and business purposes.

When the RAID operates in functional mode, the status is shown as Ready in ‘Storage Pools’.

In the event of a drive failure, you can check the drive status by the following steps:

  • When a drive fails, the turbo NAS beeps for 1.5 sec.
  • The status LED flashes Red continuously.
  • In the storage Pool section, check the RAID group. The volume status shows in degraded mode.

To install a new drive to rebuild RAID 5, follow these steps:

  • Prepare a new hard drive to rebuild RAID configuration. The capacity of the new drive should be at least the same or more than the failed drive.
  • Install the drive in Turbo NAS. It will beep at first. The status LED alternates between green and red.
  • In the storage Pool section, the status shows as Rebuilding and progress bar is shown.

The new disk volume information is shown in System logs.

Using RAID as a backup

RAID array can be used as a raid backup server with backup software. If you have a Mac Pro with some external drives connected to it, you can connect RAID array by Thunderbolt or USB 3. You can change the configuration of backup software so that it copies data to RAID array.

Raid backup server offers extra protection for your backup over what you would have on a single drive. If any of the drives fails, device software will warn you and you can swap raid backup drives and this will ensure that your backups are reliable every time. This will prevent any occurrence of unreadable backup when your computer drive fails. However, using RAID alone as a backup might not be a good idea. Below are some of the problems you might encounter by using RAID as a backup alone:

  • Suppose one day you find a corrupted file on your data server. According to the principle of RAID 1, the corrupted file was instantly saved on all drives including the RAID drive. So, all copies of the file are destroyed. However, if you use some other reliable backup, the moment a file gets corrupted, its copy will still remain safe on the raid backup server.
  • In case of virus attack, if there is some file deletion on the data server, similar is replicated on all the RAID disk arrays. So, the backup comes to no use in case of an accident.

To have all the drives in a single unit powered by the same electric supply and controller cannot be safe at all. In case of a power surge, all the disks might get damaged. But this does not mean that you should not use RAID, just back it up properly.

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