It was in 2001 when about a third of all german internet sites were offline for a week with a complete dataloss on many of them. Optionally you can add an SSD to extend the readcache but this is much slower than RAMbased caching. Some ZFS systems have 64-512 GB RAM what means that most or nearly all reads for current data are delivered from RAM. More is faster as it is used as Readcache. Oracle where ZFS is native with a 64bit Solaris claims a minumum of 2GB for ZFS solutions with any poolsize. Even with dozens of disks in a ZFS Raid-Z2/3 CPU load is not really relevant today.Ĥ GB RAM is ok for ZFS. The little raid calculation does not matter. With enough RAM and a modern CPU this is even faster than a hardwareraid with less and slower RAM. A nice extra are snaps and the advanced cache mechanism and sync write options that are part of ZFS. So the best solution would be not using Raid-6 with ext4 but using ZFS with a more robust raid than Raid-6 and with a better overall datasecurity due checksums and CopyOnWrite. No partly updated filesystem or raid-arrays - 100% crash resistent by design. The other solution are softwareraid and CopyOnWrite filesystems as there a write is done completely (data, metadata, raidstripe) or not at all. One is a hardware raidcontroller + BBU that can reduce the problem. There are two common ways to handle this. "Write hole" phenomenon in RAID5, RAID6, RAID1, and other arrays. This is due the write hole problem on Raid-6 On a crash during a write you are in danger of a corrupted filesysten and/or raid array. The RAID array will even survive the second failure when using RAID 6.With any Raid-6 solution, does not matter if softwareraid or hardwareraid, a raid stripeset is written disk by disk sequentially. You will still lose all of your data if a drive fails again. However, if a disc in a RAID 5 fails, rebuilding takes many hours. This calls for a minimum of four discs, and the likelihood of two drives failing simultaneously is, of course, extremely remote. The principle of RAID 5 is used in RAID 6, but the parity data is written to two drives instead. One disc failure is also acceptable at this level. RAID 5 adds parity to the array, which requires a total of one disk’s worth of space. However, it requires at least three discs and boosts read speeds while degrading write performance. It gives the advantages of both RAID 0 and RAID 1, offering a fair balance between security, speed, and performance. The most popular and secure RAID level is RAID 5. Distributed parity is not utilized in RAID 4. There are additional similarities to RAID 3, although all parity data is restricted to a single disc. In essence, RAID 4 stripes data at the byte level rather than the block level. Any recorded block is written to a parity disc for every row of written data. They are put on discs after being separated into blocks. The primary distinction is how data is shared. It enables data recovery in the event of failure by correctly computing the remaining bytes and parity bytes that correspond with them. The configuration information is broken down into discrete bytes and then saved to disk. We can refer to it as “the parity disc” because it is used to store hash algorithms and supports a specific processor in parity code calculation. Similar to RAID 0, RAID 3 includes a second disc in the array but expressly uses byte-level striping. Synchronizing all drives is essential while RAID 2 is in use. ![]() Every disc in RAID 2 functions as a single disc with a capacity equal to the total capacity of all data storage discs. ![]() The logarithm of the number of discs that are protecting the mentioned data is equal to the number of discs in RAID 2 that are employed to store data. With RAID 2, every bit of data is striped and written to a different drive or stripe. ![]() Because all data is written twice, the biggest drawback is that the effective storage capacity is only half of the overall drive capacity. It provides up to twice the reading performance of a single drive but does not speed up writing. If a drive dies, the controller uses the mirror drive for data recovery and ongoing operation. RAID 1 uses two drives to produce a mirror, which means that everything on each of them is identical. Mission-critical systems shouldn’t use it. All of the data in the RAID 0 array is lost if one drive fails. However, it offers no protection in the event of a drive failure and will raise the risk of a data disaster. The read/write performance and storage capacity are improved over a single drive by employing two or more drives simultaneously. RAID 0 is regarded as the most fundamental RAID level. There are numerous popular RAID configurations.
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