How long does it take to detect array parameters?

RAID recovery time

RAID recovery time depends on both the time required to read a sample of data from a disk set and the time for analyzing the data sample and determining the array configuration parameters. However, read and analysis speeds depend on many other aspects and the resulted RAID recovery time will be limited by the worst of the components.

Statistical analysis time

The RAID recovery time depends directly on the data being analyzed. Based on some data the confident decision can be obtained immediately, while the other data can be absolutely useless for determining the parameters.

On top of that, it is practically beneficial to scan the disk not in a continuous pattern. Instead, the samples are picked randomly from a disk set.

These two factors together lead to the fact that the RAID recovery time can be different each time you run ReclaiMe Free RAID Recovery. In a successful scenario, the RAID can be recovered in minutes, in the worst case it will take several hours to complete recovery.

Disk throughput

RAID recovery involves reading a lot of data. In worst case, the entire disk set is to be read three times - for the RAID analysis, then for the filesystem analysis, and then when the files are copied out. The hardware setup affects the read speed significantly. Reconfiguring the storage subsystem can sometimes reduce recovery time by the factor of ten.

The following considerations apply:

1. If you connect the disk to a SATA port on motherboard, you get 30 to 50 MB/sec throughput. A modern hard drive can deliver data faster, but realistic processing speed does not exceed 50 MB/sec with a rotational hard drive. The throughput is defined per SATA port, meaning that if you have two drives connected to SATA ports, data is processed twice as fast as long as CPU can handle it.
2. If you use USB, make sure everything works in at least USB 2.0 mode. USB 1.1 is unacceptably slow for data recovery use; however, the USB 1.1 hubs are still produced. USB 3.0 devices are not very stable as of spring 2012. You should probably avoid USB 3.0 hubs till at least 2013. Anyway, if something goes wrong with an USB 3.0 device, it falls back to USB 2.0 mode, so you don't lose much.
3. USB 2.0 provides about 15 MB/sec throughput per root port. If you connect several hard drives to an USB hub, their combined throughput is limited to 15 MB/sec.
4. If you use multiple disk image files during RAID recovery, you should evenly distribute these image files across as many physical hard drives as possible. There is a singificant penalty associated with mechanical disk seeks if you put multiple images onto one hard drive.

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Compatibility with other data recovery software

Unfortunately, there is no standard format to input the RAID parameters to data recovery software. In addition, no data recovery tool we know of has an ability to load .XML file with the RAID parameters.

Due to lack of a common standard, we have developed our own elements and attributes for the .XML file to which all the recovered RAID parameters are saved.

So we have implemented a feature to ReclaiMe Free RAID Recovery to provide the detailed instructions on how to transfer the recovered array parameters to most known RAID-capable data recovery software.

As of now, the step-by-step instructions are available for R-Studio, File Scavenger, UFS Explorer, and Zero Assumption Recovery software. If you have some other data recovery software and need the instructions, 

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RAID XML format description

ReclaiMe RAID XML format

ReclaiMe Free RAID Recovery provides an option to save the results to the .XML file. You can do this by clicking Save layout to file button, once the analysis of the RAID is completed. You should then select file name and specify a location to save the file.

There are the following elements and attributes in the .XML file:

• <disk> element, defining a member disk, for which all of the following attributes must be defined
  • path - the value can be one of the following
    • "" (empty string) for a missing disk, that is, missing RAID 5 member.
    • "\\.\PhysicalDriveN" for a physical disk, following a Windows CreateFile() notation for physical hard drives.
    • a fully qualified disk image file name, e.g. "W:\RAID\RAID-5-01-disk.img".
  • offset - offset on the disk at which the array data starts.
  • numsectors - the number of sectors on the member disk.
  • serial - the serial number of the member disk, if available. The serial number is provided for your reference only. When the XML file is loaded, it is the path which specifies the device, not the serial number.
• <RAID0> element, which defines a RAID 0 array. It has one attribute
  • blocksize - the size of the block in sectors of 512 bytes.
• <RAID5> element, which defines a RAID 5 array. It uses the following attributes
  • blocksize - the size of the block in sectors of 512 bytes.
  • layout - either "sync" for a synchronous RAID or "async" for an asynchronous RAID.
  • parity - the number of the disk (column) in the array at which parity starts. For a "right" array the attribute value is 0, for a "left" array of N disks the value is (N-1).
  • rotation - is the index difference between parity columns in two consecutive rows. Either "1" for a "right" array or "N-1" for a N-disk "left" array.
  • delay (optional) - the number of data blocks per parity block. Default value is "1". See Delayed Parity for more details.
  • firstdelay (optional) - the number of data blocks in the first delayed parity block. If omitted, the value of delay is assumed. See Delayed Parity for more details.
• <RAID6> element, which defines a RAID 6 array. It has the same set of attributes as RAID 5 plus two more parameters:
  • PQ - defines how Q parity blocks are located as to P parity blocks. This attribute can be either Qtop or Ptop.
  • WidePace - optional parameter applied only for the arrays created by Promise controller. If present, must be equal to "2".

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ReclaiMe Free RAID Recovery toolbar buttons Disks

ReclaiMe Free RAID Recovery toolbar buttons

Disks

When you click the button, the window with three columns, Device name, Capacity, and Serial number, is displayed.

For the physical disks in the Device name column, "Disk N" will be displayed, where N is the disk number as listed in Disk Management, along with the disk model name. The Serial number contains a serial number for each physical disk connected to the computer.

For the devices connected via USB, in the Capacity column near the size value, "[USB]" will be displayed. In most cases, no serial number is available.

For the disk image files the full disk image file name is displayed in the Device name column. The Serial number column is blank.

Open disk image

Allows you to open the previously created disk image file of the RAID member disk.

Create disk image

Allows you to create the disk image file of the member disk and save it to the specified location.

Start RAID 0

The button becomes available when you select a minimum of two member disks. By clicking the button, recovery of the RAID parameters for RAID 0, RAID 0+1, and RAID 1+0 is launched.

Start RAID 5

You need to select a minimum of two member disks to enable the button. Although RAID 5 requires a minimum of three disks, ReclaiMe Free RAID Recovery software is capable of recovering the parameters for RAID 5 with one missing member disk, based on the array redundancy.

Note that once the RAID recovery process is started, only Stop and Help buttons are active. Keep in mind that clicking the Stop button returns to the disk list, and all the results are discarded.

Other RAIDs

Click this button if you want to recover RAID10, RAID5E or RAID6. You need to select at least two disks for RAID5E recovery, and three disks for RAID10 and RAID6 recovery.

Stop

When you launch the program, the button is disabled. It becomes available only when recovery of the array parameters is started. Clicking the button results in the program returns to the disk selection tab, but not to the results.

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RAID recovery limitations

ReclaiMe Free RAID recovery limitations

There are either general limitations concerning all the types of RAID array like the requirement to have the same offset of data on the member disks or specific limitations applied to a particular RAID layout.

General limitations

1. If the array data is stored not from the very start of the disk, but with a certain offset, the offset is required to be the same on all disks. All known hardware controllers and NAS devices satisfy this requirement.
2. A disk set should belong to a single array. If there were several arrays on a set of disks, then it is required that one of the arrays should be significantly larger than others. A NAS device contains operating system data (usually Linux or sometimes Windows Embedded) on the same disks. Nevertheless, it is possible to recover RAID because operating system data takes up much less space on the array as compared to user data.
3. It is impossible to recover empty or almost empty array using ReclaiMe Free RAID Recovery software. The less data is stored on the array, the more time it takes to complete the analysis, and the less reliable RAID configuration parameters are derived. Each member disk, including missing disks in RAID5/6/10/1E, must contain at least 10-20GB of data.
4. Allowed block sizes are from 0.5KB (512 bytes, one sector) to 1MB.

Layout-specific limitations

RAID 0 - It is required to have all the member disks.

RAID 10

• Generally, a RAID10 survives a multiple disk failure without data loss. However, a disk set must contain at least one copy of each data block.
• ReclaiMe Free RAID Recovery is capable of recovering RAID 10 near and interleaved.
• If an array is almost empty (less than 30% filled with data), recovery time and memory use may increase significantly.

RAID 1E

• ReclaiMe Free RAID Recovery can recover only RAID 1E far arrays.

RAID 10 far and RAID 1E far

These RAID layouts consist of two different RAID0 arrays of the same size which are located on the same disk set one by one. If all the member disks are available, it is possible to use HPA/DCO to reduce size of disks in half and then recover RAID0 from the visible part of disks.

RAID 5 and RAID 5E

• One member disk may be missing.
• An array must be one of the following layouts:
  • synchronous left,
  • synchronous right,
  • asynchronous left,
  • asynchronous right.
• It is not allowed to have parity shift other than by one column per row.
• ReclaiMe Free RAID Recovery software recovers configuration parameters for the arrays with delayed parity. Allowed delay values are from 2 to 32 including those values that are not powers of two.
• RAID 5 must use even parity, i.e. XOR of all bits in a complete row (including parity bit) must be zero.

RAID 6

• ReclaiMe Free RAID Recovery only supports RAID6 based on Reed-Solomon parity function (Q). Certain controllers use their proprietary methods of calculating parity, like Vertical XOR. The list ofincompatible controllers includes, but may be not limited to
  • Adaptec RAID 3405, 3805, 3085, 31205, 31605, ICP5045BL, ICP5085BL, ICP5805BL, ICP5125BR, ICP6165BR,
  • Adaptec RAID 4800SAS, 4805SAS, ICP9085LI, ICP5085BR,
  • Adaptec SATA II RAID 2420SA, 2820SA, ICP9047MA, ICP9087MA,
  • Adaptec SCSI RAID 2130SLP, 2230SLP, ICP9014RO, ICP9024RO.
• Depending on how second parity function (Q) is calculated, sometimes all member disks are required (for RAID6 built using a Promise controller). In other cases, no more than one member disk may be missing.
• Despite of the fact that RAID6 survives failure of two member disks, ReclaiMe Free RAID Recovery is not able to recover RAID configuration parameters in this case.
• RAID 6 analysis requires a lot of computation and ReclaiMe Free RAID Recovery can use up to eight CPUs or cores, if available.

Hot spare

Hot spare drives must not be included in the list of analyzed disks. The only exception is RAID 10 for which hot spare presence doesn't influence the result of RAID recovery.

Special cases

ReclaiMe Free RAID Recovery works in some exotic cases, when other software does not:

• Delayed parity which is widely used on HP SmartArray controllers.
• RAID 5 with block size of one sector (JMicron JMB393 SATA port multiplier and other similar hardware RAID controllers).
• Promise RAID 6 with its awesome Q function computation.
• Promise RAID 1E interleaved.

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RAID Recovery usage,