Invalidating snapshot unable to allocate exception

Details are in Chapter 3, Changes to the Firebird API and ODS.

提供了对任意一个Logical Volume(LV)做“快照”(snapshot)的功能,以此来获得一个分区的状态一致性备份。在某一个状态下做备份的时候,可能有应用正在访问某一个文件或者数据库,这就是使得备份的时候文件处于一个状态,而备份完后,文件却处于另外一个状态,从而造成备份的非一致性,这种状态恢复数据库数据几乎不会成功。状态的解决办法是将其分区挂载为只读,然后通过数据库的表级别锁定(table-level write locks)甚至停止数据库来备份数据。所有这些方法无意严重影响了服务的可用性。使用LVM snapshot既可以获得一致性备份,又不会影响服务器的可用性。要提醒一点是,snapshot这种方法仅对LVM有效,对于非LVM文件系统无效。snapshot的实现有多种方式(参考文章最后的连接),这里说说LVM中snapshot的“写时复制”(copy on write) 的实现方法。当一个snapshot创建的时候,仅拷贝原始卷里数据的元数据(meta-data)。创建的时候,并不会有数据的物理拷贝,因此snapshot的创建几乎是实时的,当原始卷上有写操作执行时,snapshot跟踪原始卷块的改变,这个时候原始卷上将要改变的数据在改变之前被拷贝到snapshot预留的空间里,因此这个原理的实现叫做写时复制(copy-on-write)。在写操作写入块之前,Co W讲原始数据移动到 snapshot空间里,这样就保证了所有的数据在snapshot创建时保持一致。而对于snapshot的读操作,如果是读取数据块是没有修改过的,那么会将读操作直接重定向到原始卷上,如果是要读取已经修改过的块,那么就读取拷贝到snapshot中的块。这样,通常的文件I/0流程有一个改变,那就是在文件系统和设备驱动之间增加了一个cow层,变成了下面这个样子:file I/0 --- block I /O下面的图也许可以比较容易了解Co W的原理:采取Co W实现方式时,snapshot的大小并不需要和原始卷一样大,其大小仅仅只需要考虑两个方面:从shapshot创建到释放这段时间内,估计块的改变量有多大;数据更新的频率。一旦 snapshot的空间记录满了原始卷块变换的信息,那么这个snapshot立刻被释放,从而无法使用,从而导致这个snapshot无效。所以,非常重要的一点,一定要在snapshot的生命周期里,做完你需要做得事情。当然,如果你的snapshot大小和原始卷一样大,甚至还要大,那它的寿命就是“与天齐寿”了。snapshot其实除了备份以外,还有很多其他用途1)虚拟化在使用 LVM2 时,快照可以不是只读的。这意味着,在创建快照之后, 可以像常规块设备一样挂载和读写快照。因 为流行的虚拟化系统(比如 Xen、VMWare、Qemu 和 KVM)可以将块设备用作 guest 映像,所以可以创建这些映像的完整拷贝,并根据需要使用它们,它们就像是内存占用量很低的虚拟机。这样做的好处是部署迅速(创建快照的时间常常不超过几秒)和节省空间(guest 共享原映像的大多数数据)。设置的步骤如下: 1.

As usual with patch releases, this sub-release fixes bugs addressed since the previous patch release.

During the 18 months that have passed since Firebird 2.1.3, this latest release takes benefits from some improvements deriving from the ongoing development of forward full release versions.

Please burn me with knowledge if this is a known problem ;).

Thanks, Stephan Kernel log: --- Mar 18 orlok kernel: device-mapper: snapshots: Invalidating snapshot: Unable to allocate exception.

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Secondly, as soon as the fs size is somewhat =4G solves/worksaround the problem.1.34.1-7 program options library for C ii libboost-regex1.34.1 1.34.1-7 regular expression library for C ii libc6 2.7-9 GNU C Library: Shared libraries ii libgcc1 1:4.3.0-1 GCC support library ii liblockdev1 1.0.3-1.2 Run-time shared library for lockin ii libpam0g 0.99.7.1-6 Pluggable Authentication Modules l ii libstdc 6 4.3.0-1 The GNU Standard C Library v3 ii libuuid1 1.40.8-2 universally unique id library ii schroot-common 1.1.6-1 common files for schroot schroot recommends no packages. schroot only calls the "lvcreate" command, as you could do from the command-line, and then mounts the newly-created device. `- GPG Public Key: 0x25BFB848 Please GPG sign your mail. Ok, for the record, this is how to reproduce leaving out schroot and fs, just using lvm commands. Before testing this, please NOTE that (at least when having fs mounted !!

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