计算机的存储系统一直是链条中最慢的组件。您的CPU具有快速缓存，它与RAM的交互速度要慢得多（但仍然很快！），然后我们有您的系统磁盘，它们再次慢了几个数量级。
RAID或Redundant Array of Independent/Inexpensive Disks是一种将多个磁盘组合成一个以提高性能、可靠性或两者兼而有之的方法。随着SSD(SSDs)迅速取代机械硬盘，这为我们提供了一个选择：HDD Raid Vs SSD Raid。这里没有绝对的赢家，所以让我们仔细看看考虑因素。
RAID 级别回顾(A Recap Of RAID Levels)
虽然RAID(RAID)配置没有通用标准，但有几个所谓的RAID “级别”已经变得相当普遍。当我们将HDD RAID技术与SSD RAID技术进行比较时，重要的是要回顾一下每种(SSD RAID)RAID设置所需的优缺点和驱动器数量。让我们简要介绍一下它们：
- RAID 0 需要两个磁盘，不提供冗余，但速度快且不占用磁盘空间
- RAID 1 需要两个磁盘，提供冗余，但只有很小的速度提升和 50% 的磁盘空间损失
- RAID 10 需要四个磁盘，提供冗余，提供快速读取、更好的写入速度并牺牲 50% 的磁盘空间。
当然还有其他更复杂的RAID级别（例如 1E、5、50、6 和 60），但这三个是典型用户最感兴趣的。
HDD RAID 与单个 SSD(HDD RAID Vs a Single SSD)
我们认为，人们可能想知道RAID以及它与SSD(SSDs)的关系的最常见原因来自于这个特定的比较。因此，我们将首先解决这个问题。
机械硬盘驱动器非常慢，因此获得更好吞吐量的一种流行方法是将两个相同的驱动器组合到RAID 0配置中。数据在两个驱动器上“条带化”，它们充当一个硬盘驱动器，但（理论上）传输速度是其两倍。由于每个驱动器都有数据的独特部分，因此您始终可以让两个驱动器参与任何操作。
可悲的是，在原始速度方面，单个SSD总是会胜过 RAID 0 硬盘设置。即使是最快、最昂贵的 10,000 RPM SATA III消费级硬盘也只能达到 200MB/s。理论上(In theory)。所以他们中的两个在RAID0中只能管理不到两倍。
几乎任何SATA III SSD都将非常接近 600MB/s 的连接极限。如果我们说的是使用PCIe协议的(PCIe)NVME SSD，那么典型的读取速度会超过 2000MB/s。
换句话说，如果您正在寻找纯粹的性能，那么单个SSD将始终胜过一对机械驱动器。即使它们是世界上最快的机械驱动器。
可靠性和数据保护也是如此。如果您的RAID 10设置带有四个硬盘，您仍然可以获得双倍的驱动器速度，并且您可以丢失一个驱动器而不会丢失任何数据。尽管如此，单个SSD仍将是更可靠的解决方案。SSD的写入次数有限，无法再覆盖现有数据，但您仍然可以读取磁盘上的所有数据。
SSD的自发故障非常罕见，但您始终可以选择在RAID 1中运行两个(RAID 1)SSD。没有显着的速度优势，但一个驱动器可以完全失败而不会丢失数据。我们不建议纯粹为了数据安全而花钱购买RAID 1 SSD设置。(SSD)将硬盘映像简单地备份到经济实惠的外部驱动器或云中更具成本效益，因为大多数桌面系统都不是关键任务。
HDD RAID 与 SSD RAID：一般注意事项(HDD RAID vs SSD RAID: General Considerations)
现在我们已经处理了单个SSD场景，让我们谈谈直接RAID到RAID的比较。也就是说，RAID 中的机械驱动器与RAID中(RAID)的SSD(SSDs)相比。需要考虑三个主要方面：性能、价格和数据可靠性。让我们更详细地看看每一个。
表现(Performance)
听到SSD RAID配置在原始性能方面总是优于任何机械驱动器RAID设置，您可能不会感到惊讶。(RAID)真正的问题是在RAID中运行(RAID)SSD(SSDs)可以获得多少性能以及是否值得。这是一个复杂的问题。
一个因素是硬件与软件RAID。专用硬件RAID控制器将提供比基于软件的解决方案更好的性能。此外，随着速度的提高，计算机中的其他组件可能会成为限制因素或“瓶颈”。
例如，在日常使用中，SATA III SSD和M.2 NVMe PCIe驱动器之间几乎没有区别。尽管后者快了五六倍。游戏(Games)加载速度并没有明显加快，应用程序也不一定更活泼。另一方面，诸如视频编辑或涉及大量数据集分析的专业应用程序之类的工作负载将占用您必须提供的带宽。
这意味着将两个SSD(SSDs)放入RAID 0可能不会改善平均用户体验，而成本可以更好地用于系统的其他地方
Price!
尽管SSD(SSDs)在过去几年中价格下降了很多，但按每 GB 计算，它们仍然比机械驱动器贵很多倍。事实上，机械驱动器最近一直在提升容量，因为它们无法在性能上与之竞争。
这使得SSD(SSDs)作为冗余大容量存储没有吸引力。纯冗余或冗余和高性能RAID配置中的机械驱动器对于桌面用户来说仍然非常重要且具有成本效益。如果您运行家庭NAS（网络附加存储）系统进行流媒体或文件共享，这是最实用的选择。
如果您绝对需要RAID 0中两个(RAID 0)SSD(SSDs)的速度，或者拥有一个受益于RAID 1的任务关键型驱动器，那么您的价格是运行单个驱动器的两倍。只有您可以决定 200% 的成本是否值得任一选项的优势。
可靠性和耐用性(Reliability & Endurance)
SSD 耐用性(SSD endurance)是我们之前写过的东西，它是与机械驱动器的复杂比较。SSD(SSDs)写入过多时会磨损。然而，对于现代驱动器，写入耐久性远远超出了大多数用户所需要的。
即使无法写入SSD，也不太可能完全丢失数据。在许多方面存在RAID，因为机械驱动器首先容易出现故障。正面交锋，SSD(SSDs)更加可靠，以至于它们不会使冗余RAID引人注目。
没有明确的答案(No Clear Answers)
正如您所看到的，答案永远不会是HDD RAID或SSD RAID（或其他）。这非常取决于您的特定需求。尽管如此，我们可以提供一些通用的指导方针：
- 大多数用户不会从SSD RAID速度改进中受益。
- HDD RAID仍然是大容量存储的最佳选择。
- SSD(SSDs)足够可靠，使RAID仅适用于关键任务用途。
清楚地了解每种方法在哪里最有效，您应该更好地了解哪种选择对您来说最实用和最经济。
HDD Raid Vs SSD Raid: The Major Differences You Should Know
Thе storage system of a сomputer has always been the slowest component in the chain. Your CPU has fast cache memory, which interacts much slower (yet still fast!) with RAM and then we have your systems disks, which are again orders of magnitude slower.
RAID or Redundant Array of Independent/Inexpensive Disks is a method of combining multiple disks into one to improve performance, reliability or both. With SSDs quickly taking over from mechanical hard drives, this presents us with a choice: HDD Raid Vs SSD Raid. There’s no absolute winner here, so let’s take a close look at the considerations.
A Recap Of RAID Levels
While there is no universal standard for RAID configurations, there are several so-called RAID “levels” that have become pretty commonplace. When we’re comparing HDD RAID technology against SSD RAID technology, it’s important to recap the pros, cons and number of drives you need for each type of RAID setup. Let’s go over them in short order:
- RAID 0 needs two disks, provides no redundancy but lots of speed and no disk space penalty
- RAID 1 needs two disks, provides redundancy, but only small speed gains and a 50% disk space penalty
- RAID 10 needs four disks, provides redundancy, provides fast reads, better write speeds and sacrifices 50% of disk space.
There are of course other more complex RAID levels (e.g. 1E, 5, 50, 6 & 60) but these three are the most common that typical users would be interested in.
HDD RAID Vs a Single SSD
We figure the most common reason someone might be wondering about RAID and how it relates to SSDs comes from this specific comparison. So we’ll get this one out of the way first.
Mechanical hard drives are pretty slow, so one popular way to get better throughput is by combining two identical drives into the RAID 0 configuration. The data is “striped” across both drives and they act as one hard drive, but with (theoretically) twice the transfer speed. Since each drive has a unique part of your data, you can always have both drives contributing to any operation.
Sadly, when it comes to raw speed, a single SSD is always going to win out against a RAID 0 hard drive setup. Even the fastest, most expensive 10,000 RPM SATA III consumer hard drive only tops out at 200MB/s. In theory. So two of them in RAID0 would only manage a little under twice that.
Just about any SATA III SSD will get very close to the limit of the connection at 600MB/s. If we’re talking NVME SSDs using the PCIe protocol, then typical read speeds exceed 2000MB/s.
In other words, if pure performance is what you’re looking for, a single SSD will always beat a pair of mechanical drives. Even if they are the fastest mechanical drives in the world.
The same goes for reliability and data protection. If you have a RAID 10 setup with four hard drives, you still get double the drive speed and you can lose a drive without losing any data. Despite this, a single SSD will still be a more reliable solution. SSD have a limited number of writes before they can no longer overwrite existing data, but you can still read all the data on the disk.
Spontaneous failure of an SSD is incredibly uncommon, but you always have the option of running two SSD in RAID 1. There’s no significant speed benefit, but one drive can fail completely without data loss. We wouldn’t recommend spending money on a RAID 1 SSD setup purely for data safety. It’s far more cost-effective to simply back up your hard drive image to an affordable external drive or the cloud, since most desktop systems are not mission critical.
HDD RAID vs SSD RAID: General Considerations
Now that we’ve dealt with the single SSD scenario, let’s talk about direct RAID-to-RAID comparisons. That is, mechanical drives in RAID compared to SSDs in RAID. There are three main aspects to consider: performance, price and data reliability. Let’s look at each one in more detail.
Performance
You will probably be unsurprised to hear that an SSD RAID configuration will always beat any mechanical drive RAID setup in raw performance. The real question is how much performance you’ll gain from running SSDs in RAID and whether it’s worth it. This is a complicated question.
One factor is hardware versus software RAID. A dedicated hardware RAID controller will provide better performance than a software-based solution. Additionally, as speed increases, other components in your computer might become a limiting factor or “bottleneck”.
For example, in day-to-day use there’s little difference between a SATA III SSD and an M.2 NVMe PCIe drive. despite the latter being five or six times faster. Games don’t load noticeably faster and applications aren’t necessarily more snappy. Workloads such as video editing or professional applications involving massive dataset analysis, on the other hand, will eat as much bandwidth as you have to offer.
This means that putting two SSDs in RAID 0 probably won’t improve the average user experience and the cost could be better spent elsewhere in the system
Price!
Although SSDs have come down a lot in price over the last few years, they are still many times more expensive on a per-gigabyte basis than mechanical drives. In fact, mechanical drives have been pushing capacity of late since they can’t compete on performance.
This makes SSDs unattractive as redundant mass storage. Mechanical drives in purely-redundant or redundant and performance RAID configurations are still very relevant and cost effective for desktop users. If you run a home NAS (network attached storage) system for streaming or file sharing, it’s the most practical choice.
If you absolutely need the speed of two SSDs in RAID 0 or have a mission critical drive that benefits from RAID 1, you’re looking at twice the price of running a single drive. Only you can decide if 200% of the cost is worth the advantages of either option.
Reliability & Endurance
SSD endurance is something we’ve written about before and it’s a complex comparison with mechanical drives. SSDs wear out when they’ve been written to too much. However for modern drives, write endurance is far beyond what most users will ever need.
A complete loss of data even when an SSD cannot be written to, is very unlikely. In many ways RAID exists because mechanical drives are prone to failure in the first place. Head to head, SSDs are so much more reliable that they don’t make redundant RAID compelling.
No Clear Answers
As you can see, there is no situation where the answer will always be HDD RAID or SSD RAID (or otherwise). It’s very dependent on your specific needs. Nonetheless, we can provide some general guidelines:
- Most users won’t benefit from SSD RAID speed improvements.
- HDD RAID is still best for mass storage.
- SSDs are reliable enough to make RAID sensible only for mission-critical uses.
With a clear picture of where each approach works best, you should have a much better idea which option makes the most functional and economic sense for you.
