壓縮磁碟後反而空間不足?
 

今天同事問我
無法複製檔案的問題

硬碟是250GB SSD
全部資料夾容量只占200GB
剩4X多GB
從隨身碟複製10GB進去
卻出現空間不足
查看後發現同事有開磁碟壓縮

自己做實驗
win10環境
設定一個1GB RAMDISK
打開磁碟壓縮
複製一堆檔案約650MB進去
複製快結束時出現空間不足 無法複製

經查看
已複製進去約598MB 磁碟大小 391MB
剩下約50MB還沒複製
理論上沒有空間不足的問題

打開RAMDISK磁碟內容
發現
已使用空間約 0.99GB
可用空間 只剩5.46MB

全選檔案查看內容或用Treesize查看
全部檔案加起來也只有約600MB左右

當然解決方法就是不要用磁碟壓縮
不過 怎麼會這樣呢?
有人知道嗎? 謝謝。

SSD有不可使用的預留空間

https://kknews.cc/zh-tw/digital/bgmnpb6.html

謝謝回答
我用RAMDISK也是一樣
所以不是這問題

看這篇

https://docs.microsoft.com/en-us/ar...tfs-compression

最下面有提到出現磁碟已滿的問題(注意第3點)

Disk full error during a backup read operation or file copy…

1. NTFS determines which compression unit is being accessed.
2. The compression unit’s entire allocated range is read.
3. If the unit is not compressed, then we skip to step 5. Otherwise, NTFS would attempt to reserve (but not allocate) the space required to write the decompressed CU back to disk. If insufficient free space exists on the disk, then the application might get an ERROR_DISK_FULL during the read.
4. The CU would be decompressed in memory.
5. The decompressed byte range would be mapped into cache and returned to the requesting application.
6. If part of the CU is altered in cache…
----a. The reserved disk space from step 3 would become allocated space.
----b. The CU contents would be compressed and flushed back to the newly allocated region (the LCN location will usually not change).
----c. Any recoverable disk space within the CU would be freed.

謝謝您的回答
有些收穫
這邊也有類似的討論
https://superuser.com/questions/605...-a-lot-of-space