RAID

RAID is intended to keep your dedicated servers or your virtual private server (VPS) alive and your data redundant in case of single (or more) disk failures – allowing you to replace faulty hardware in the case of disk failure.

Our own opinion is that RAID is always worth the extra cost – it usually saves you from a lot of trouble when things go wrong. There are two main options to decide between when you want a RAID setup, these are software and hardware RAID. In the first case, your main CPU/memory take over the part of ensuring your desired RAID level, in the latter, you have extra (costly) hardware to handle that part of your machine.

Software RAID has advantages such as being cheaper and not subjecting you to vendor lock-in, and – in some cases – even outperforms a hardware RAID with today’s fast CPUs. Nevertheless, hardware RAID offers features a software RAID setup cannot, for example hot swapping disks, or write back caching if you have a BBU.

This post is not about the pros and cons of software vs. hardware RAID, however. Essentially, we want to present the four most common setups for data redundancy and integrity – RAID 1, RAID 5, RAID 6, and Raid 10 – in a concise summary.

RAID 1 is all about disk mirroring. You team up two identical disks, and they form a mirror, all your data is kept twice. You can lose one disk and still go on running your server. Of course, the storage efficiency is rather low – out of 2x2TB you only get 2TB in total.

RAID 5 is another very common setup. It needs at least 3 disks, and in a nutshell, you can lose one disk before things start getting sinister for your server. That gives you moderate storage efficiency – in a 3x2TB setup you get around 4TB in total, in a 4x2TB you get something close to 6TB in total.

RAID 6 could be seen as a further development of RAID 5, in laymen’s terms. Here you need at least 4 disks, and you can afford 2 disks going down before your disk array suffers data loss. The storage efficiency is worse than with RAID 5, but typically better than with RAID 1 since both RAID 5 and RAID 6 allow for more than just 3 or 4 disks to be used.

And finally, RAID 10 is a mix of RAID 0 (stripes over several disks) in combination with RAID 1 (mirroring). This gives the same capacity as RAID 1, as well as the same redundancy level, but requires at least 4 disks to work and is generally more expensive than RAID 5 or 6 compared to their capacity.

In terms of performance, RAID 10 generally outperforms the other RAIDs in terms of write speed. This difference becomes smaller with more disks in the array, but still, in your typical 4 disk setup, RAID 10 is fastest for writes, and RAID 1 is typically faster for writes than RAID 5 or 6 as well. In terms of read performance, RAID 1 lags behind the other options, whereas RAID 5, 6, and 10 can be considered pretty similar and vary depending on the applications and I/O going on.

Overall, if you don’t need much storage and want a cheap redundant solution, choose RAID 1, it offers enough performance for everyday’s applications as well. If you need more redundancy, but do not have write intensive applications, then RAID 5 or RAID 6 are fine. DB-intensive (really intensive in terms of writes) applications should consider RAID 10, however. The increase in write performance is well worth the extra cost, but pay attention to the number of disks in the array – the more disks in a RAID 5 or RAID 6 array, the better write performance becomes.

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