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Written by users of the FreeNAS® network-attached storage operating system.
Copyright © 2011-2015 iXsystems
本手册涵盖 FreeNAS® 9.3 安装和使用。
FreeNAS® 用户手册仍在完善，依赖于许多人的贡献。如果你愿意帮助完善手册，请您查阅 README 。如果你使用 IRC Freenode，欢迎加入 #freenas 频道，在这里你可以找到更多 FreeNAS® 用户。
FreeNAS® 用户手册允许您在 创作共享署名授权协议 下共享和再发行。你可以在 iXsystems 所发布手册的基础上复制、发行、翻译。
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FreeNAS® 9.3 用户手册采用下列排版方式：
FreeNAS® 是一个基于 FreeBSD 开发的嵌入式开源网络附加存储 network-attached storage (NAS) 操作系统，在 BSD license 授权许可协议下发布。NAS 是一种专门为文件共享和存储优化的操作系统。
FreeNAS® 9.3 修复的 BUG 。
从9.3版本开始，FreeNAS® 采用 “滚动发布” 替代传统单点发布模式。新的 更新 机制使得系统安全修复、BUG修复和增加新功能变得非常简单。由于一些更新营销到了WebGUI界面，因此在这里罗列9.3-RELEASE开始发生的一些变化。
Since FreeNAS® 9.3 is based on FreeBSD 9.3, it supports the same hardware found in the FreeBSD Hardware Compatibility List . Supported processors are listed in section 2.1 amd64 . Beginning with version 9.3, FreeNAS® is only available for 64-bit (also known as amd64) processors.
beginning with version 9.3, FreeNAS® boots from a GPT partition. This means that the system BIOS must be able to boot using either the legacy BIOS firmware interface or EFI.
Actual hardware requirements will vary depending upon what you are using your FreeNAS® system for. This section provides some guidelines to get you started. You can also skim through the FreeNAS® Hardware Forum for performance tips from other FreeNAS® users or to post questions regarding the hardware best suited to meet your requirements. This forum post provides some specific recommendations if you are planning on purchasing hardware. Refer to Building, Burn-In, and Testing your FreeNAS system for detailed instructions on how to test new hardware.
The best way to get the most out of your FreeNAS® system is to install as much RAM as possible. The recommended minimum is 8 GB of RAM. The more RAM, the better the performance, and the FreeNAS® Forums provide anecdotal evidence from users on how much performance is gained by adding more RAM.
Depending upon your use case, your system may require more RAM. Here are some general rules of thumb:
If your system supports it and your budget allows for it, install ECC RAM. While more expensive, ECC RAM is highly recommended as it prevents in-flight corruption of data before the error-correcting properties of ZFS come into play, thus providing consistency for the checksumming and parity calculations performed by ZFS. If you consider your data to be important, use ECC RAM. This Case Study describes the risks associated with memory corruption.
If you don’t have at least 8GB of RAM, you should consider getting more powerful hardware before using FreeNAS® to store your data. Plenty of users expect FreeNAS® to function with less than these requirements, just at reduced performance. The bottom line is that these minimums are based on the feedback of many users. Users that do not meet these requirements and who ask for help in the forums or IRC will likely be ignored because of the abundance of information that FreeNAS® may not behave properly with less than 8GB of RAM.
The FreeNAS® operating system is installed to at least one device that is separate from the storage disks. The device can be a USB stick, compact flash, or SSD. Technically, it can also be installed onto a hard drive, but this is discouraged as that drive will then become unavailable for data storage.
if you will be burning the installation file to a USB stick, you will need two USB slots, each with an inserted USB device, where one USB stick contains the installer and the other USB stick is selected to install into. When performing the installation, be sure to select the correct USB device to install to. In other words, you can not install FreeNAS® into the same USB stick that you boot the installer from. After installation, remove the USB stick containing the installer, and if necessary, configure the BIOS to boot from the remaining USB stick.
When determining the type and size of device to install the operating system to, keep the following points in mind:
The Disk section of the FreeBSD Hardware List lists the supported disk controllers. In addition, support for 3ware 6gbps RAID controllers has been added along with the CLI utility tw_cli for managing 3ware RAID controllers.
FreeNAS® supports hot pluggable drives. To use this feature, make sure that AHCI is enabled in the BIOS.
If you need reliable disk alerting and immediate reporting of a failed drive, use an HBA such as a LSI MegaRAID controller or a 3Ware twa-compatible controller. More information about LSI cards and FreeNAS® can be found in this forum post .
Suggestions for testing disks before adding them to a RAID array can be found in this forum post .
This article provides a good overview of hard drives which are well suited for a NAS.
If you have some money to spend and wish to optimize your disk subsystem, consider your read/write needs, your budget, and your RAID requirements:
If you have the budget and high performance is a key requirement, consider a Fusion-I/O card which is optimized for massive random access. These cards are expensive and are suited for high-end systems that demand performance. A Fusion-I/O card can be formatted with a filesystem and used as direct storage; when used this way, it does not have the write issues typically associated with a flash device. A Fusion-I/O card can also be used as a cache device when your ZFS dataset size is bigger than your RAM. Due to the increased throughput, systems running these cards typically use multiple 10 GigE network interfaces.
If you will be using ZFS, Disk Space Requirements for ZFS Storage Pools recommends a minimum of 16 GB of disk space. Due to the way that ZFS creates swap, you can not format less than 3 GB of space with ZFS . However, on a drive that is below the minimum recommended size you lose a fair amount of storage space to swap: for example, on a 4 GB drive, 2 GB will be reserved for swap.
If you are new to ZFS and are purchasing hardware, read through ZFS Storage Pools Recommendations first.
ZFS uses dynamic block sizing, meaning that it is capable of striping different sized disks. However, if you care about performance, use disks of the same size. Further, when creating a RAIDZ*, only the size of the smallest disk will be used on each disk.
The Ethernet section of the FreeBSD Hardware Notes indicates which interfaces are supported by each driver. While many interfaces are supported, FreeNAS® users have seen the best performance from Intel and Chelsio interfaces, so consider these brands if you are purchasing a new NIC. Realteks will perform poorly under CPU load as interfaces with these chipsets do not provide their own processors.
At a minimum, a GigE interface is recommended. While GigE interfaces and switches are affordable for home use, modern disks can easily saturate 110 MB/s. If you require higher network throughput, you can bond multiple GigE cards together using the LACP type of Link Aggregations . However, the switch will need to support LACP which means you will need a more expensive managed switch.
If network performance is a requirement and you have some money to spend, use 10 GigE interfaces and a managed switch. If you are purchasing a managed switch, consider one that supports LACP and jumbo frames as both can be used to increase network throughput. Refer to the 10 Gig Networking Primer for more information.
at this time the following are not supported: InfiniBand, FibreChannel over Ethernet, or wireless interfaces.
If network speed is a requirement, consider both your hardware and the type of shares that you create. On the same hardware, CIFS will be slower than FTP or NFS as Samba is single-threaded . If you will be using CIFS, use a fast CPU.
Wake on LAN (WOL) support is dependent upon the FreeBSD driver for the interface. If the driver supports WOL, it can be enabled using ifconfig(8) . To determine if WOL is supported on a particular interface, specify the interface name to the following command. In this example, the capabilities line indicates that WOL is supported for the re0 interface:
ifconfig -m re0 re0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 mtu 1500 options=42098<VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,WOL_MAGIC,VLAN_HWTSO> capabilities=5399b<RXCSUM,TXCSUM,VLAN_MTU,VLAN_HWTAGGING,VLAN_HWCSUM,TSO4,WOL_UCAST,WOL_MCAST, WOL_MAGIC,VLAN_HWFILTER,VLAN_H WTSO>
If you find that WOL support is indicated but not working for a particular interface, create a bug report using the instructions in Support .
ZFS is an advanced, modern filesystem that was specifically designed to provide features not available in traditional UNIX filesystems. It was originally developed at Sun with the intent to open source the filesystem so that it could be ported to other operating systems. After the Oracle acquisition of Sun, some of the original ZFS engineers founded OpenZFS in order to provided continued, collaborative development of the open source version. To differentiate itself from Oracle ZFS version numbers, OpenZFS uses feature flags. Feature flags are used to tag features with unique names in order to provide portability between OpenZFS implementations running on different platforms, as long as all of the feature flags enabled on the ZFS pool are supported by both platforms. FreeNAS® uses OpenZFS and each new version of FreeNAS® keeps up-to-date with the latest feature flags and OpenZFS bug fixes.
Here is an overview of the features provided by ZFS:
ZFS is a transactional, Copy-On-Write (COW) filesystem. For each write request, a copy is made of the associated disk block(s) and all changes are made to the copy rather than to the original block(s). Once the write is complete, all block pointers are changed to point to the new copy. This means that ZFS always writes to free space and most writes will be sequential. When ZFS has direct access to disks, it will bundle multiple read and write requests into transactions; most filesystems can not do this as they only have access to disk blocks. A transaction either completes or fails, meaning there will never be a write-hole and a filesystem checker utility is not necessary. Because of the transactional design, as additional storage capacity is added it becomes immediately available for writes; to rebalance the data, one can copy it to re-write the existing data across all available disks. As a 128-bit filesystem, the maximum filesystem or file size is 16 exabytes.
ZFS was designed to be a self-healing filesystem . As ZFS writes data, it creates a checksum for each disk block it writes. As ZFS reads data, it validates the checksum for each disk block it reads. If ZFS identifies a disk block checksum error on a pool that is mirrored or uses RAIDZ*, ZFS will fix the corrupted data with the correct data. Since some disk blocks are rarely read, regular scrubs should be scheduled so that ZFS can read all of the data blocks in order to validate their checksums and correct any corrupted blocks. While multiple disks are required in order to provide redundancy and data correction, ZFS will still provide data corruption detection to a system with one disk. FreeNAS® automatically schedules a monthly scrub for each ZFS pool and the results of the scrub will be displayed in View Volumes . Reading the scrub results can provide an early indication of possible disk failure.
Unlike traditional UNIX filesystems, you do not need to define partition sizes at filesystem creation time . Instead, you feed a certain number of disk(s) at a time (known as a vdev) to a ZFS pool and create filesystems from the pool as needed. As more capacity is needed, identical vdevs can be striped into the pool. In FreeNAS®, Volume Manager can be used to create or extend ZFS pools. Once a pool is created, it can be divided into dynamically-sized datasets or fixed-size zvols as needed. Datasets can be used to optimize storage for the type of data being stored as permissions and properties such as quotas and compression can be set on a per-dataset level. A zvol is essentially a raw, virtual block device which can be used for applications that need raw-device semantics such as iSCSI device extents.
ZFS supports real-time data compression . Compression happens when a block is written to disk, but only if the written data will benefit from compression. When a compressed block is accessed, it is automatically decompressed. Since compression happens at the block level, not the file level, it is transparent to any applications accessing the compressed data. By default, ZFS pools made using FreeNAS® version 9.2.1 or later will use the recommended LZ4 compression algorithm.
ZFS provides low-cost, instantaneous snapshots of the specified pool, dataset, or zvol. Due to COW, the initial size of a snapshot is 0 bytes and the size of the snapshot increases over time as changes to the files in the snapshot are written to disk. Snapshots can be used to provide a copy of data at the point in time the snapshot was created. When a file is deleted, its disk blocks are added to the free list; however, the blocks for that file in any existing snapshots are not added to the free list until all referencing snapshots are removed. This means that snapshots provide a clever way of keeping a history of files, should you need to recover an older copy of a file or a deleted file. For this reason, many administrators take snapshots often (e.g. every 15 minutes), store them for a period of time (e.g. for a month), and store them on another system. Such a strategy allows the administrator to roll the system back to a specific time or, if there is a catastrophic loss, an off-site snapshot can restore the system up to the last snapshot interval (e.g. within 15 minutes of the data loss). Snapshots are stored locally but can also be replicated to a remote ZFS pool. During replication, ZFS does not do a byte-for-byte copy but instead converts a snapshot into a stream of data. This design means that the ZFS pool on the receiving end does not need to be identical and can use a different RAIDZ level, volume size, compression settings, etc.
ZFS boot environments provide a method for recovering from a failed upgrade . Beginning with FreeNAS® version 9.3, a snapshot of the dataset the operating system resides on is automatically taken before an upgrade or a system update. This saved boot environment is automatically added to the GRUB boot loader. Should the upgrade or configuration change fail, simply reboot and select the previous boot environment from the boot menu. Users can also create their own boot environments in System ‣ Boot as needed, for example before making configuration changes. This way, the system can be rebooted into a snapshot of the system that did not include the new configuration changes.
ZFS provides a write cache in RAM as well as a ZFS Intent Log (ZIL). The ZIL is a temporary storage area for synchronous writes until they are written asynchronously to the ZFS pool. If the system has many synchronous writes where the integrity of the write matters, such as from a database server or when using NFS over ESXi, performance can be increased by adding a dedicated log device, or slog, using Volume Manager . More detailed explanations can be found in this forum post and in this blog post . A dedicated log device will have no affect on CIFS, AFP, or iSCSI as these protocols rarely use synchronous writes. When creating a dedicated log device, it is recommended to use a fast SSD with a supercapacitor or a bank of capacitors that can handle writing the contents of the SSD’s RAM to the SSD. The zilstat utility can be run from Shell to help determine if the system would benefit from a dedicated ZIL device. See this website for usage information. If you decide to create a dedicated log device to speed up NFS writes, the SSD can be half the size of system RAM as anything larger than that is unused capacity. The log device does not need to be mirrored on a pool running ZFSv28 or feature flags as the system will revert to using the ZIL if the log device fails and only the data in the device which had not been written to the pool will be lost (typically the last few seconds of writes). You can replace the lost log device in the View Volumes ‣ Volume Status screen. Note that a dedicated log device can not be shared between ZFS pools and that the same device cannot hold both a log and a cache device.
ZFS provides a read cache in RAM, known as the ARC, to reduce read latency. FreeNAS® adds ARC stats to top(1) and includes the arc_summary.py and arcstat.py tools for monitoring the efficiency of the ARC. If an SSD is dedicated as a cache device, it is known as an L2ARC and ZFS uses it to store more reads which can increase random read performance. However, adding an L2ARC is not a substitute for insufficient RAM as L2ARC needs RAM in order to function. If you do not have enough RAM for a good sized ARC, you will not be increasing performance, and in most cases you will actually hurt performance and could potentially cause system instability. RAM is always faster than disks, so always add as much RAM as possible before determining if the system would benefit from a L2ARC device. If you have a lot of applications that do large amounts of random reads, on a dataset small enough to fit into the L2ARC, read performance may be increased by adding a dedicated cache device using Volume Manager . SSD cache devices only help if your active data is larger than system RAM, but small enough that a significant percentage of it will fit on the SSD. As a general rule of thumb, an L2ARC should not be added to a system with less than 64 GB of RAM and the size of an L2ARC should not exceed 5x the amount of RAM. In some cases, it may be more efficient to have two separate pools: one on SSDs for active data and another on hard drives for rarely used content. After adding an L2ARC, monitor its effectiveness using tools such as arcstat . If you need to increase the size of an existing L2ARC, you can stripe another cache device using Volume Manager . The GUI will always stripe L2ARC, not mirror it, as the contents of L2ARC are recreated at boot. Losing an L2ARC device will not affect the integrity of the pool, but may have an impact on read performance, depending upon the workload and the ratio of dataset size to cache size. Note that a dedicated L2ARC device can not be shared between ZFS pools.
ZFS was designed to provide redundancy while addressing some of the inherent limitations of hardware RAID such as the write-hole and corrupt data written over time before the hardware controller provides an alert. ZFS provides three levels of redundancy, known as RAIDZ*, where the number after the RAIDZ indicates how many disks per vdev can be lost without losing data. ZFS also supports mirrors, with no restrictions on the number of disks in the mirror. ZFS was designed for commodity disks so no RAID controller is needed. While ZFS can also be used with a RAID controller, it is recommended that the controller be put into JBOD mode so that ZFS has full control of the disks. When determining the type of ZFS redundancy to use, consider whether your goal is to maximize disk space or performance:
The following resources can also help you determine the RAID configuration best suited to your storage needs:
NO RAID SOLUTION PROVIDES A REPLACEMENT FOR A RELIABLE BACKUP STRATEGY. BAD STUFF CAN STILL HAPPEN AND YOU WILL BE GLAD THAT YOU BACKED UP YOUR DATA WHEN IT DOES. See Periodic Snapshot Tasks and Replication Tasks if you would like to use replicated ZFS snapshots as part of your backup strategy.
While ZFS provides many benefits, there are some caveats to be aware of:
If you are new to ZFS, the Wikipedia entry on ZFS provides an excellent starting point to learn more about its features. These resources are also useful to bookmark and refer to as needed: