Fix typos and grammar

Optimization.md

@@ -9,7 +9,7 @@ When starting volume server, you can specify the index type. By default it is us
 
 In some Linux file system, e.g., XFS, ext4, Btrfs, etc, SeaweedFS can optionally allocate disk space for the volume files. This ensures file data is on contiguous blocks, which can improve performance when files are large and may cover multiple extents. 
 
-To enable disk space preallcation, start the master with these options on a Linux OS with supporting file system.
+To enable disk space preallcation, start the master with these options on a Linux OS with a supporting file system.
 ```
   -volumePreallocate
     	Preallocate disk space for volumes.
@@ -51,7 +51,7 @@ copy_other = 1            # create n x 1 = n actual volumes
 
 Same as above, more volumes will increase read concurrency.
 
-In addition, increase the replication will also help. Having the same data stored on multiple servers will surely increase read concurrency.
+In addition, increasing the replication will also help. Having the same data stored on multiple servers will surely increase read concurrency.
 
 ## Add more hard drives
 
@@ -65,7 +65,7 @@ The SeaweedFS usually only open a few actual disk files. But the network file re
 
 For each volume server, there are 2 things impacts the memory requirements.
 
-By default, the volume server uses in memory index to achieve O(1) disk read. Roughly about 20 bytes is needed for each file. If one 30GB volume has 1 million files of averaged 30KB, the volume can cost 20MB memory to hold the index. You can also sue leveldb index to reduce memory consumption and speed up startup time. To use it, "weed server -volume.index=[memory|leveldb|leveldbMedium|leveldbLarge]", or "weed volume -index=[memory|leveldb|leveldbMedium|leveldbLarge]". 
+By default, the volume server uses in memory index to achieve O(1) disk read. Roughly about 20 bytes is needed for each file. If one 30GB volume has 1 million files of averaged 30KB, the volume can cost 20MB memory to hold the index. You can also use leveldb index to reduce memory consumption and speed up startup time. To use it, "weed server -volume.index=[memory|leveldb|leveldbMedium|leveldbLarge]", or "weed volume -index=[memory|leveldb|leveldbMedium|leveldbLarge]". 
 
 Another aspect is the total file size that are read at the same time. If serving 100KB-sized file for 1000 concurrent reads, 100MB memory is needed. 
 
@@ -81,7 +81,7 @@ A file key has 3 parts:
 - needle id: a monotonously increasing and unique number
 - file cookie: a random number, you can customize it in whichever way you want
 
-You can directly ask master server to assign a file key, and replace the needle id part to your own unique id, e.g., user id.
+You can directly ask master server to assign a file key, and replace the needle id part with your own unique id, e.g., user id.
 
 Also you can get each volume's free space from the server status.
 
@@ -97,7 +97,7 @@ The assigned file cookie can also be customized, as long as it is 32-bit.
 
 "strict monotonously increasing" needle id is not necessary, but keeping needle id in a "mostly" increasing order helps to keep the in memory data structure efficient. 
 
-If the needle id have to be random, you can use leveldb as the index when starting volume server.
+If the needle id has to be random, you can use leveldb as the index when starting volume server.
 
 ## Upload large files