PowerScaleの1次キャッシュの容量について

tanboi_3さん

PowerScaleは1次、2次、3次キャッシュまで搭載している仕組みだと思いますが、
各モデルの1次キャッシュの容量が記載している資料などはございますでしょうか？
⇒OneFSのL1キャッシュはメモリーなどの性能にもよりますが、Node毎に存在し、Memory上に
存在します。しかしサイズに関しては可変なので一定ではありません。

実際のサイズは以下のコマンドで確認可能です。

# isi_cache_stats

例）
# isi_cache_stats
Totals             l1_data: a  35G  98% r  47G  65% p 1.4G  87%, l1_encoded: a  11G  99% r 118M  73% p  66M 100%, l1_meta: r 140G  56% p  12M  99%,
 l2_data: r 3.0G  63% p 4.3M   2%, l2_meta: r 140G 100% p  52M 100%,
l3_data: r 0.0B   0% p 0.0B   0%, l3_meta: r 0.0B   0% p 0.0B   0%

参考
OneFS Caching Hierarchy

OneFS uses up to three levels of read cache, plus an NVRAM-backed write cache, or write coalescer. The first two types of read cache, level 1 (L1) and level 2 (L2), are memory (RAM) based, and analogous to the cache used in CPUs.These two cache layers are present in all PowerScale storage nodes.

OneFS provides tools to accurately assess the performance of the various levels of cache at a point in time. These cache statistics can be viewed from the OneFS CLI using the isi_cache_stats command. Statistics for L1, L2, and L3 cache are displayed for both data and metadata. For example:

# isi_cache_stats
Totals
l1_data: a 224G 100% r 226G 100% p 318M 77%, l1_encoded: a 0.0B 0% r 0.0B 0% p 0.0B 0%, l1_meta: r 4.5T 99% p 152K 48%,
l2_data: r 1.2G 95% p 115M 79%, l2_meta: r 27G 72% p 28M 3%,
l3_data: r 0.0B 0% p 0.0B 0%, l3_meta: r 8G 99% p 0.0B 0%

Level 1 cache

Note: L1 cache is used differently in accelerator nodes, such as the PowerScale P100, which do not contain any disk drives. Instead, the entire read cache is L1 cache because all the data is fetched from other storage nodes. Also, cache aging is based on a Least Recently Used (LRU) eviction policy, as opposed to the drop-behind algorithm typically used in a storage node’s L1 cache. An accelerator’s L1 cache is large, and the data in it is highly likely to be requested again. Data blocks are not immediately removed from cache upon use. However, metadata and update-heavy workloads do not benefit as much, and an accelerator’s cache is only beneficial to clients directly connected to the node.

@tanboi_3​ さん

ご返信を有難うございます。

1次キャッシュも2次キャッシュもシステム内でそのリソースの割り振りを
適宜しているというイメージになります。

またLeast Recently Used (LRU)の法則が適応されています。

（先述の資料以下参照ください）

Level 1 cache

Note: L1 cache is used differently in accelerator nodes, such as the PowerScale P100, which do not contain any disk drives. Instead, the entire read cache is L1 cache because all the data is fetched from other storage nodes. Also, cache aging is based on a Least Recently Used (LRU) eviction policy, as opposed to the drop-behind algorithm typically used in a storage node’s L1 cache. An accelerator’s L1 cache is large, and the data in it is highly likely to be requested again. Data blocks are not immediately removed from cache upon use. However, metadata and update-heavy workloads do not benefit as much, and an accelerator’s cache is only beneficial to clients directly connected to the node.