用于存储集群拓扑的相关信息；二是etcd，用于存储文件的元数据信息。而etcd可以用于实现mds高可用，没必要引入其他组件。 使用etcd实现元数据节点的leader主要依赖于它的两个核心机制: TTL和CAS。TTL(time to live)指的是给一个key设置一个有效期，到期后key会被自动删掉。这在很多分布式锁的实现上都会用到，可以保证锁的实时性和有效性。CAS(Atomic Compare-and-Swap) sessions can participate in the election for the // same prefix, but only one can be the leader at a time. // // If the context is 'context.TODO()/context.Background()', the Campaign // will continue to be // mds t := time.Now() ctx, cancel := context.WithTimeout(context.Background(), time.Duration(int(timeout))*time.Millisecond) defer cancel()

can read and write data successfully on the other two replicas. When two copies fail at the same time, the system cannot determine the failure reason because only minor number replica is written successfully replicas is R, and the data recovery Time in the case of failed disks is T. The Annual Failure Rate of disks is AFR, and the average running Time of disks is MTBF (Mean Time Before Failure). 𝐴𝐹𝑅 = 1 fails, up to 50 other disks will restore the data on that disk at the same time. According to this, the data recovery time T can be estimated. 𝐹𝐼𝑇 = 𝐴𝐹𝑅 24 ∗ 365 The probability of failure

uint32_t btime; /* birth / create time */ uint32_t ctime; /* status change time */ uint32_t mtime; /* modify time */ uint32_t atime; /* access time */ uint32_t uid; /* user

一个目录则会打开失败。 O_DIRECTORY : 。 O_NOFOLLOW 如果pathname是一个符号链接，则会打开失败（ELOOP） : 不更新Inode中的last access time（进程uid=文件uid或者进程在它的user namespace有CAP_FOWNER, 而文件的uid在这个namespace中有一个映射）。 O_NOATIME : 在进程执行exec系统 kernel that any currently cached file data (ie., data that the filesystem provided the last time the file was open) need not be invalidated. Has no effect when set in other contexts (in FDIRDEntryInfo dentry;© XXX Page 14 of 23 int flags; int magic; struct { int last_modified_time; } write_notify; int64_t offset; //current offset } FCFSAPIFileInfo; static int do_open(fuse_req_t

the maximum size of read requests will still be * limited by the kernel. * * NOTE: For the time being, the maximum size of read requests© XXX Page 11 of 33 * must be set both here *and* passed filesystem as "congested". This instructs the kernel to * expect that queued requests will take some time to complete, and to * adjust its algorithms accordingly (e.g. by putting a waiting thread * to resolution. Filesystems supporting only second resolution * should set this to 1000000000. */ unsigned time_gran; /** * For future use.© XXX Page 14 of 33 */ unsigned reserved[22]; }; 未实现任何权限检查的文件系统通常

tend, etc in control plane. 2. Depending on libCurve, the application must be restarted every time the library is updated. To solve this problem, the CurveBS Client has been optimized to decouple

快照版本号 chunkSize uint32_t chunk的size segmentSize uint64_t segment的size fileLength uint64_t 卷的大小 time uint64_t 快照创建时间 status enum 快照的创建状态 Etcd中的快照元数据:快照的元数据和数据组织 • fileInfo 快照目的卷的卷名等信息 • chunkMap

UcpWorker实现 ●提供命令行参数调整ucp worker的行为 –--brpc_ucp_worker_busy_poll为true时使用busy poll –--brpc_ucp_worker_poll_time为wait模式时，一次突发的poll的时长 –--brpc_ucp_deliver_out_of_order为true，接收端乱序提交 –--brpc_ucp_close_flush，release