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为什么 L2ARC 没有为目录遍历提供更快的速度？

tag-icon • tag-icon cache zfs ssd directory find
为什么 L2ARC 没有为目录遍历提供更快的速度？

L2Arc 通常配置为在 SSD 上缓存随机旋转盘片读取。我设置此配置是为了加快目录遍历速度。

设置如下：

# zpool list -v
NAME   SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
geek1  2.72T  1.18T  1.54T         -    53%    43%  4.64x  ONLINE  -
  sdc  1.36T   606G   786G         -    54%    43%
  sdd  1.36T   606G   786G         -    53%    43%
log      -      -      -         -      -      -
  zil  3.97G      0  3.97G         -     0%     0%
cache      -      -      -         -      -      -
  l2arc  32.0G  4.24G  27.8G         -     0%    13%

该机器拥有 20GB 内存：对于 Arc 来说足够了。

我原本以为find文件系统上的调用会大大加快。速度提高了 5 倍，但从绝对意义上讲，它仍然很慢。列出 46M 文件需要 3.4 小时。

# while true; do time find /geek1/ -type f|wc -l; done
46774149

real    1103m18.661s
user    2m15.143s
sys     5m52.096s
46774149

real    243m0.289s
user    2m3.063s
sys     5m7.107s
46774149

real    205m23.922s
user    2m7.566s
sys     6m32.638s

如何使目录遍历更加高效？

zpool get all印刷：

NAME   PROPERTY                    VALUE                       SOURCE
geek1  size                        2.72T                       -
geek1  capacity                    43%                         -
geek1  altroot                     -                           default
geek1  health                      ONLINE                      -
geek1  guid                                                    default
geek1  version                     -                           default
geek1  bootfs                      -                           default
geek1  delegation                  on                          default
geek1  autoreplace                 off                         default
geek1  cachefile                   -                           default
geek1  failmode                    wait                        default
geek1  listsnapshots               off                         default
geek1  autoexpand                  off                         default
geek1  dedupditto                  0                           default
geek1  dedupratio                  4.64x                       -
geek1  free                        1.54T                       -
geek1  allocated                   1.18T                       -
geek1  readonly                    off                         -
geek1  ashift                      0                           default
geek1  comment                     -                           default
geek1  expandsize                  -                           -
geek1  freeing                     0                           default
geek1  fragmentation               53%                         -
geek1  leaked                      0                           default
geek1  feature@async_destroy       enabled                     local
geek1  feature@empty_bpobj         active                      local
geek1  feature@lz4_compress        active                      local
geek1  feature@spacemap_histogram  active                      local
geek1  feature@enabled_txg         active                      local
geek1  feature@hole_birth          active                      local
geek1  feature@extensible_dataset  enabled                     local
geek1  feature@embedded_data       active                      local
geek1  feature@bookmarks           enabled                     local
geek1  feature@filesystem_limits   enabled                     local
geek1  feature@large_blocks        enabled                     local

答案1

如果您在 Linux 上使用 ZFS，则速度缓慢可能取决于xattr默认设置（xattr=on），它将扩展属性存储在隐藏目录/文件中。

尝试将更改设置xattr为sa，发出类似 的命令zfs set xattr=sa <pool/fs>。但是，它只会影响新创建的文件；因此您需要删除/重新加载所有文件才能显著加快速度。

换句话说，在重新加载所有文件之前，先进行小规模尝试。

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