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In the field of data storage (computer storage), RAID is a key term. This is a technology for storing data over several disks. There are a number of different methods (schemes), but in most cases reliability and speed increase. In general, we can say that RAID combines several disks into one logical unit. Data is usually split and stored (and read) on several disks at once, thus increasing write/read speed. Furthermore, a checksum is stored on the next disk, so that data can be restored even if a certain part (disk) fails.
RAID can be created software-wise using operating system resources, which is cheap but less reliable and efficient. Or hardware-wise, where everything is managed by the controller. Nowadays, even most home computers are equipped with a controller with simple HW RAID, so it's not a problem to use RAID 0 or RAID 1.
Basic types of RAID
- RAID 0 - striping
- Minimum 2 disks, data are stored alternately in so-called strips. Simultaneous writing/reading to all disks (each time something different), both are accelerated n times. Failure of one disk means losing all data.
- RAID 1 - mirroring
- Minimum 2 disks. Reading from all at once, i.e., acceleration, the same data is written to both disks. Safe, but only part of the capacity is used.
- RAID 3 - striping with parity
- Data is added with a checksum on a separate disk. Replaced by RAID 5.
- RAID 5 - striping with distributed parity
- Minimum 3 disks. Data + parity are stored, from which damaged data can be recovered. Reading from all disks at once except parity, i.e., acceleration n-1 times. When writing, parity needs to be calculated - HW acceleration on the controller, used capacity is (n-1) times the disk size. Can handle the failure of one disk.
- RAID 6 - striping with double distributed parity
- Similar to RAID 5, but with double parity, can handle the failure of two disks at once, minimum 4 disks, capacity (n-2) times.
- RAID 10 - RAID 1 and RAID 0
- Speed of RAID 0 and safety of RAID 1, minimum 4 disks, capacity is half, faster than RAID 5.
- RAID 50 - RAID 5 and RAID 0
- Minimum 6 disks, similar to RAID 5, faster.
Related terms
- hot-swap disk
- feature of a disk array and disk that allows disk replacement while running
- hot-spare disk
- spare disk that waits for a disk failure and automatically replaces it, in some systems the hot-spare function is automatically cycled (due to load)
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Muzu se zeptat jaky RAID se nejcasteji pouziva ve firemni siti?
respond to [1]kulda: Záleží na účelu. V serveru se třeba doporučuje jiný RAID na systémových discích a jiný na datových. Dnes máme většinou vše na poli, kde děláme velký RAID přes hodně disků. Praxe asi každému ukáže, že RAID s možným výpadkem jednoho disku je nedostatečný (často při rebuildu odejde další disk, protože je hodně zatížený). Takže dost se používá RAID 6. Nebo někteří výrobci, jako NetApp, mají vlastní RAID, který doporučují.