Meanwhile, the data checksum will cross-check its corresponding metadata checksum to make sure the data checksum itself is intact. Once you enable data checksum when creating a shared folder, the Btrfs file system will calculate a checksum (data checksum) for every written file, and further protect that data checksum with another checksum (metadata checksum).Įvery time data scrubbing is conducted, the file system will recalculate the checksum and compare it with the previously stored data checksum. If any data that is inconsistent with the checksum is detected, the system will try to use the redundant copy to repair the data. This is where Btrfs data scrubbing comes in.Īs you may have noticed, not only can you see whether your RAID type supports RAID scrubbing, but you can also know if file system scrubbing is supported from the volume information under the Data Scrubbing tab in Storage Manager 1.įile system data scrubbing employs the checksum mechanism to check the volumes in the Btrfs file system. Say today we want to reconstruct Pa using A1, A2, and A3 (as shown in Function 1 above), but if any one of A1, A2, or A3 is corrupt, then performing the function will go awry, only to yield the wrong content and make things even worse. Sole reliance on RAID scrubbing may pose a potential risk. If a block is corrupted, every other block will be “consistently corrupt” as well. That is, it cannot tell which data block is incorrect. ![]() The problem is that RAID scrubbing can only ensure data consistency. This kind of errors are caused by various reasons: hardware errors, electromagnetic interference, and many more. It can occur during the write-to-drive process without being reported. We cannot make sure that the data written to the drives will always be accurate. “Will my data always remain intact if I set a regular RAID scrubbing schedule?” If it fails to fulfill the XOR function, it will be recalculated again and again until all the values are consistent. RAID scrubbing scans all the contents in an array, making sure all the parity stripes satisfy Function 1. If it proves wrong, then there’s a problem of data inconsistency because the reconstructed data will be incorrect.įailure to recover your data is something serious, so it’s vital to retain data consistency. Upon the failure of a single drive, we can use Function 2 to calculate the redundant copy and recover the contents accordingly. If it holds true, then we can safely say that the data in the array is consistent. First of all, we know that the parity information in each drive should satisfy Function 1 shown above. Now that we have a basic understanding of the characteristics of RAID 5, then we can go on to talk about data consistency. This is how RAID 5 achieves redundancy, protecting your data against drive failure. The recovered contents are what we call a redundant copy. Suppose the drive containing A2 breaks, then we can perform the following XOR calculation to reconstruct it: A2 = A1 (XOR) A3 (XOR) Pa (Function 2) If one of the drives fails, RAID 5 will repair the missing data by using Pa and contents of the remaining two drives. When writing A1, A2, and A3, RAID 5 will use the following XOR to calculate Pa and write it to the corresponding block. What about Pa, Pb, and Pc? They are parity blocks distributed across the drives. Likewise, it reads data in the same order. When writing a block of sequential data into the array, for example, RAID 5 will write it into A1, A2, A3, B1, B2, B3 in sequence. RAID 5 : It requires at least three drives and utilizes parity striping at the block level. ![]() Here we’re going to briefly introduce RAID 5. Simply put, it combines multiple drives into a single storage pool, offering fault tolerance and data redundancy. RAID stands for redundant array of independent disks. Read on to see how data scrubbing prevents your digital assets from data corruption.īefore we go into detail about data scrubbing, let us introduce RAID arrays to you first. The two images below are the original photo and the corrupt one that suffers from bit rot. It could be a real disaster if it happens to one of your precious photos capturing the indelible memories. Worse still, they occur silently without any warning. As times goes by, some data may fall victim to slow degradation that gradually deteriorates data integrity. Small steps to big protection for your storageĭata scrubbing, as the name suggests, is a process of inspecting volumes and modifying the detected inconsistencies.
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