![]() There would be a very good argument made for a small drive array dedicated to the OS and application data that would be cumbersome to reinstall in case of array loss being kept on RAID 1 and the RAID 0 data array being separate from it. It should be noted that an exception to the "One Big Array" approach that would be common is in systems using RAID 0 for data. The only downside of RAID 0 is that it is fragile and provides no protection against data loss in case of drive failure or even an unrecoverable read error (URE, which would cause data corruption the same as a desktop drive faces). It is very fast, very simple and provides the most cost effective capacity. In these cases the obvious choice is RAID 0. This could be a case where downtime is not a problem and data is static or nearly so and rather than spending to reduce downtime we only worry about protecting the data via backup mechanisms so that if an array fails we simply restore the array completely. This is common for reconstructable data such as working space for rendering, intermediary calculation spaces, or caches - situations where spending money to protect data is wasted and it would be acceptable to simply recreate lost data rather than protecting it. There are many times where data saved to disk is considered ephemeral and does not need to be protected. This may sound like an odd thing to consider but it is a very important scenario. The first scenario we should consider is if your data does not matter. None of these choices are at all reckless and at worst they are overly conservative. But the idea here is to cover the vast majority of cases with tried and true approaches that are designed around modern equipment, use cases, and needs while being mindful to err on the side of safety-when a choice is less than ideal it is still safe. The goal of this guide is general rules of thumb to allow any IT Pro to build a safe and reliable storage system. Rules of thumb do not and cannot cover every scenario because exceptions always exist. Array splitting is far more likely to cause harm rather than good. Only in situations where careful study of the storage needs and heavy analysis are being done should we look at array splitting. ![]() The need or desire to split our storage into multiple, physical arrays is mostly gone today and should only be done in non-general circumstances. That is a single RAID array on which all system and data partitions are created. In general we use what is termed a "One Big Array" approach. The rate of change in the industry has dropped significantly since that time and these recommendations are likely to stand for a very long time, very possibly until spindle-based drive storage is no longer available or at least popular, but like all things predictions are subject to great change. Good RAID design of 1998 is very poor RAID design today. Over the past two decades the common approaches to RAID storage have changed dramatically and while it is not anticipated that the key factors that influence these decisions will change enough in the future to alter these recommendations, it is very possible that they will. The guidance here is written for standard systems in 2015. Storage systems larger than roughly twenty five spindles should not work from standard guidance but delve deeper into specific storage needs to ensure proper planning. ![]() We will not tackle solid state drives as these have very different characteristics and require their own guidance. For the purposes of this guide we will assume storage projects of no more than twenty five traditional drives (spinning platter drives properly known as Winchester drives.) These drives could be SFF (2.5") or LFF (3.5") commonly, SATA or SAS, consumer or enterprise. My goal here is to provide a handy guide that will allow a non-storage practitioner to approach RAID decision making in a practical and, most importantly, safe way. While the work on this subject is nearly staggering the information can be distilled into a handful of common, practical storage approaches that will cover nearly all use cases. A truly monumental amount of information abounds in reference to RAID storage systems exploring topics such as risk, performance, capacity, trends, approaches, and more. ![]()
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