17.6. 一些例子
Vinum 维护着一个描述以一个独立系统为目标 配置数据库的。最初，用户通过vinum(8) 工具的帮助从一个或多个配置文件创建配置数据库。Vinum 在它的控制 下在每个磁盘(Vinum 叫 device) 上存储一个 它的配置数据库的拷贝。这个数据库在每个状态变化的时候被升级， 以便能精确地回复每个Vinum 目标的状态。
17.6.1. 配置文件
配置文件描述了独立的 Vinum.一个简单卷的定义可能是这样的:
drive a device /dev/da3h
volume myvol
plex org concat
sd length 512m drive a
这个文件描述了四个Vinum 目标:
-
drive 行描述了一个磁盘分区（驱动器） 和与下面的硬件相关的它的位置。它给出了一个符号名 a. 这个与设备名称分开的符号名允许 磁盘从一个位置移动到另一个位置而不会搞混。
-
volume 行描述了一个卷。 唯一的必须属性是名称，在这个例子中是 myvol.
-
plex 行定义了一个plex。 唯一需要的参数是组织,在这个例子中是 concat. 没有名称是必然的: 系统自动通过添加suffix .pxpx 来从卷名称产生一个名字,这里的x 是在卷中的plex 的编号。而这个plex 将被 叫做myvol.p0。
-
sd 行描述了一个subdisk。 最小的说明是存储subdisk 的驱动器名称，和subdisk 的长度。 对于plex，没有名称也是必然的：系统自动通过添加 suffix .sx 来分配源自plex 的名称，这里 x是plex 中subdisk 的编号。 Vinum 给这个subdisk 命名为myvol.p0.s0。
处理完这个文件后, vinum(8)会产生下面的输出：
# vinum -> create config1
Configuration summary
Drives: 1 (4 configured)
Volumes: 1 (4 configured)
Plexes: 1 (8 configured)
Subdisks: 1 (16 configured)
D a State: up Device /dev/da3h Avail: 2061/2573 MB (80%)
V myvol State: up Plexes: 1 Size: 512 MB
P myvol.p0 C State: up Subdisks: 1 Size: 512 MB
S myvol.p0.s0 State: up PO: 0 B Size: 512 MB
这个输出显示了vinum(8)简要的列表格式。 图图形 17-4中它用图形来表示这一点。
下面这个图显示了一个由按顺序排列的subdisk 组成的plex。 在这个小小的例子中，卷包含一个plex，plex 包含一个subdisk。
这个特殊的卷与一个传统的磁盘分区没有什么特别的优势。 下面的章节会描述到几个非常有趣的配置方法。 This particular volume has no specific advantage over a conventional disk partition. It contains a single plex, so it is not redundant. The plex contains a single subdisk, so there is no difference in storage allocation from a conventional disk partition. The following sections illustrate various more interesting configuration methods.
17.6.2. 增强的可靠性：镜象
The resilience of a volume can be increased by mirroring. When laying out a mirrored volume, it is important to ensure that the subdisks of each plex are on different drives, so that a drive failure will not take down both plexes. The following configuration mirrors a volume:
drive b device /dev/da4h
volume mirror
plex org concat
sd length 512m drive a
plex org concat
sd length 512m drive b
In this example, it was not necessary to specify a definition of drive a again, since Vinum keeps track of all objects in its configuration database. After processing this definition, the configuration looks like:
Drives: 2 (4 configured)
Volumes: 2 (4 configured)
Plexes: 3 (8 configured)
Subdisks: 3 (16 configured)
D a State: up Device /dev/da3h Avail: 1549/2573 MB (60%)
D b State: up Device /dev/da4h Avail: 2061/2573 MB (80%)
V myvol State: up Plexes: 1 Size: 512 MB
V mirror State: up Plexes: 2 Size: 512 MB
P myvol.p0 C State: up Subdisks: 1 Size: 512 MB
P mirror.p0 C State: up Subdisks: 1 Size: 512 MB
P mirror.p1 C State: initializing Subdisks: 1 Size: 512 MB
S myvol.p0.s0 State: up PO: 0 B Size: 512 MB
S mirror.p0.s0 State: up PO: 0 B Size: 512 MB
S mirror.p1.s0 State: empty PO: 0 B Size: 512 MB
图形 17-5 shows the structure graphically.
In this example, each plex contains the full 512 MB of address space. As in the previous example, each plex contains only a single subdisk.
17.6.3. Optimizing Performance
The mirrored volume in the previous example is more resistant to failure than an unmirrored volume, but its performance is less: each write to the volume requires a write to both drives, using up a greater proportion of the total disk bandwidth. Performance considerations demand a different approach: instead of mirroring, the data is striped across as many disk drives as possible. The following configuration shows a volume with a plex striped across four disk drives:
drive c device /dev/da5h
drive d device /dev/da6h
volume stripe
plex org striped 512k
sd length 128m drive a
sd length 128m drive b
sd length 128m drive c
sd length 128m drive d
As before, it is not necessary to define the drives which are already known to Vinum. After processing this definition, the configuration looks like:
Drives: 4 (4 configured)
Volumes: 3 (4 configured)
Plexes: 4 (8 configured)
Subdisks: 7 (16 configured)
D a State: up Device /dev/da3h Avail: 1421/2573 MB (55%)
D b State: up Device /dev/da4h Avail: 1933/2573 MB (75%)
D c State: up Device /dev/da5h Avail: 2445/2573 MB (95%)
D d State: up Device /dev/da6h Avail: 2445/2573 MB (95%)
V myvol State: up Plexes: 1 Size: 512 MB
V mirror State: up Plexes: 2 Size: 512 MB
V striped State: up Plexes: 1 Size: 512 MB
P myvol.p0 C State: up Subdisks: 1 Size: 512 MB
P mirror.p0 C State: up Subdisks: 1 Size: 512 MB
P mirror.p1 C State: initializing Subdisks: 1 Size: 512 MB
P striped.p1 State: up Subdisks: 1 Size: 512 MB
S myvol.p0.s0 State: up PO: 0 B Size: 512 MB
S mirror.p0.s0 State: up PO: 0 B Size: 512 MB
S mirror.p1.s0 State: empty PO: 0 B Size: 512 MB
S striped.p0.s0 State: up PO: 0 B Size: 128 MB
S striped.p0.s1 State: up PO: 512 kB Size: 128 MB
S striped.p0.s2 State: up PO: 1024 kB Size: 128 MB
S striped.p0.s3 State: up PO: 1536 kB Size: 128 MB
This volume is represented in 图形 17-6. The darkness of the stripes indicates the position within the plex address space: the lightest stripes come first, the darkest last.
17.6.4. Resilience and Performance
With sufficient hardware, it is possible to build volumes which show both increased resilience and increased performance compared to standard UNIX® partitions. A typical configuration file might be:
volume raid10
plex org striped 512k
sd length 102480k drive a
sd length 102480k drive b
sd length 102480k drive c
sd length 102480k drive d
sd length 102480k drive e
plex org striped 512k
sd length 102480k drive c
sd length 102480k drive d
sd length 102480k drive e
sd length 102480k drive a
sd length 102480k drive b
The subdisks of the second plex are offset by two drives from those of the first plex: this helps ensure that writes do not go to the same subdisks even if a transfer goes over two drives.
图形 17-7 represents the structure of this volume.
