PTT首發連載 低階格式化與壞軌之真相(2) - 儲存設備

By Suhail Hany
at 2010-07-25T10:27
at 2010-07-25T10:27
Table of Contents
什麼叫壞軌?這其實是錯誤說法 ,因為硬碟最小單位為Sector (LBA) 扇區, 一次最小單
位就為 256 Sectors ( LBA)
因此嚴格來說應該叫壞扇區
軟體怎樣判定壞扇區?
我們來看看經典軟體MHDD 怎樣去檢驗扇區的
1. MHDD sends VERIFY SECTORS command with LBA number and
number of sectors to verify as parameters
2. DRIVE raises BUSY flag
3. MHDD starts timer
4. After drive executes VERIFY command, it drops BUSY flag
5. MHDD counts the time and puts corresponding block
on the screen. If error occures MHDD prints corresponding
letter which describes the error.
也就是根據回應時間來做磁區品質好壞的分別.
ATA讀取錯誤會有下面的原因
1. 假性損壞:ECC 校驗碼與該Sector 不合
2. 物理損傷 :磁頭或磁介質損壞
3. 拒絕訪問:加密扇區或是硬碟軔體區有問題
ECC 校驗錯誤是由于扇區數據 與該扇區的校驗值不對應,通常就被報告為校驗錯誤(
ECC Error)
可用 Zero Fill 處理.對扇區寫0 和重寫校驗值。Zero fill 過程中將每個扇區的所有
字節全部寫0,並將每個扇區的校驗值也寫回初始值,這樣可以將部分缺陷糾正過來。
寫零後就很有可能將扇區數據與該扇區的校驗值重新對應起來,而達到"修復"該扇區的功
效。
Zero Fill也可處理少量物理扇區損壞,因為本身硬碟內 Smart 機制在發現壞扇區時, 會
啟用通用的自動替換扇區(Automatic reallocation sector),對該扇區進行替換,並
且記錄Glist 內 。 但是當故障扇區的容量Glist 滿時,此硬碟就無法再做sector
remapping中量磁道進行重新編號。
所以千萬要瞭解,低階格調化軟體不是真正修正壞扇區.
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儲存設備
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