In this article we will consider the basic types of hard drives for servers: how they differ and whether they should be necessarily from the server manufacturer’s brand. Server hard drive should always be ready to respond to many requests with minimal latency and to provide a high level of data integrity.
The server hard disk drive must meet stringent requirements:
- Reliability – unrecoverable data loss can result in multi-million dollar and reputational losses
- Performance – servers are designed to handle multiple requests
- Response Time – users don’t have to wait until the server disk “awaken” and process their requests
There are 4 major categories (excluding SSD, SAS SSD, PCI-e SSD) hard drives:
- SATA (ordinary SATA) – spindle speed 5400 and 7200 rpm (revolutions per minute)
- SATA RAID Edition (SATA RE) – spindle speed of 7200 rpm, with support of RAID-controller commands
- SAS Near Line (SAS NL) – rotational frequency 7200 rpm
- SAS Enterprise – spindle speed 10000 or 1500 rpm
At first you need to decide what type of the connection interface you want – SATA or SAS.
SATA or SAS?
The SATA interface is a further modification of the IDE, which was later renamed to PATA. This interface is initially focused for the use on home computers as well as industrial systems with moderate requirements for performance and reliability. At the same time, SAS is the successor of the classic server SCSI interface.
Initially SAS interface has more bandwidth than SATA. But in the third generation, SATA III has a maximum bandwidth of 6 Gb/s, as well as the second generation of SAS. Nowadays servers with a third-generation SAS-controller is available, with a bandwidth up to 12 Gbit/s.
For connection, SAS-disk server must be equipped with the appropriate controller. This provides backward compatibility interfaces to SAS-controller can be connected to the SATA-drives, and makes vice versa impossible.
SAS provides full-duplex communication: the hard drive at the same time handle two commands (one read and one write command), and SATA-drive – either to read or write. But this advantage is only noticeable, when you are using large number of disks, if you compare SAS NL and SATA RE.
If bring intermediate results, SATA-drives are good for creating bulk storage, which will not require maximum performance. And in case you need a fast disk subsystem, your best choice is SAS.
Say No to the ordinary hard drives
Usual SATA drives are not designed for use in servers. There are several reasons:
- Low vibration resistance
- High level of non-recoverable error
- No support for hardware RAID-controller commands
Of course, the cost of ordinary desktop SATA is significantly lower than that of the server, and nothing prevents their use for small tasks that do not require high performance from disk subsystem. If the integrity and access speed to data is on the first place, it is still strongly recommended to take the server hard drives.
Server hard drives have several meaningful differences:
- Reinforced spindle shaft more resistant to external influences
- Additional vibration control
- Technology, significantly increasing positioning accuracy, and the height of the flight above the heads
- Rich self-diagnostics allow timely notify about imminent disk failure
Non-recoverable error level
Another important difference of the server hard drives – level of unrecoverable error. Ordinary SATA is about 10-14. It means that while you overwriting 2 TB drive 6 times, you will almost certainly get one unrecoverable error. For home disks it is not a problem, but if you need to overwrite the database each month, then 6 months later it can be damaged. For SAS disks level of non-recoverable error even lower – it is 10-16 , for SATA RE / SAS NL – 10-15.
For example, the following table contains the value of the probability of error on rebuild for the different types of drives configured in RAID Level 5 array.
|600 GB Drive||1 TB Drive|
|SATA RE / SAS NL||2,4%||4%|
Note. Potential for error is proportional to the number of drives into a RAID-array.
How does SAS-disk provided a lower error rate?
- The size of the sector on the SATA-disks – 512 bytes, on SAS-drives – 520 bytes. Additional 8 bytes are used for parity verification
- Other reading algorithms
- Advanced data recovery algorithms without controller
The myth about the brands
Finally, the most important question: do you need to buy a brand drives? There is no secret that HP, IBM and DELL do not produce hard drives. They buy them from third-party manufacturers, and then test them, reflash and put their logos on them.
One hand, these drives have several advantages:
- Firmware considers features of controllers of various server models
- Additional quality control and stress tests reduce the probability of purchasing drives with hidden defects
- Vendor warranty and full support is available for the “brand” drives
But “native” hard drives are about two or three times more expensive than the same model, but with the logos of manufacturers – Seagate, Western Digital, Toshiba, HGST. We are sure, that such difference in price is not justified for all the promises of increased reliability.
As the practice shows, the “non-native” hard drives operate without difficulties on:
- HP servers – at least from Gen 6
- IBM servers – at least with the M2 generation
- DELL servers – from 10 generations
According to the statistics, most reliable are Hitachi drives. In second place Western Digital, on the third – Seagate.
Сheck your warranty
If you decided not to to buy “non-native” hard disks, at first you must ask the seller: who provides the warranty? It is the fact, that many stores do not provide a guarantee on the hard disks, referring to the manufacturer’s warranty. But there is a subtle point: for example, some models of Seagate warranty period starts from the date of production. So do not exclude the situation that you can purchase a brand new drives, which is over the manufacturer warranty.
Before purchasing, you can check the warranty of specific instances on the manufacturers’ websites:
- Seagate: http://support.seagate.com/customer/en-US/warranty_validation.jsp
- Western Digital: http://support.wdc.com/Warranty/warrantyStatus.aspx?lang=en
- Hitachi: https://www.hgst.com/portal/site/en/support/warranty
When choosing a hard drive, at first you need to start from the tasks to be performed by the server:
- If you do not need high-speed access and reliable data storage, and the number of discs will not exceed 4, we strongly recommend you choose the SATA RAID Edition drives. This is a great choice for low-cost entry-level servers, that serving a small number of users.
- If the server hold the database or the number of disks in the array will be 5 or more, it is better to choose SAS NL. Oftenly, these discs are placed in servers, that is used in medium-sized companies: under the accounting system, CMS, corporate repositories.
- If you need maximum performance and/or reliability of data storage, for example, in the processing of financial transactions, your best choice is SAS Enterprise drives. It supports for high-servers with a large number of users as well as for systems, which is operating with the most important data.