這些天，我們所有人都經(jīng)常面對SMR(疊瓦式磁性記錄)硬盤數(shù)據(jù)恢復(fù)。 從本文中，您將了解它們的真正含義，SMR和PMR驅(qū)動器之間的區(qū)別，如何繞過SMR驅(qū)動器中的問題以及如何使用PC-3000 Portable III / Express / UDMA獲得數(shù)據(jù)訪問權(quán)限。
These days we all very often face modern SMR drives. From this article, you will find out what they actually are, what the difference between SMR and PMR drives is, how to bypass issues in SMR drives and get data access with the?PC-3000 Portable III?/?Express?/?UDMA?Systems.
先講一點理論。A bit of theory to begin with.
帶狀磁記錄(SMR)技術(shù)將每片磁道的數(shù)量增加25%。通過在磁頭中使用讀取器可獲得更高的密度，該讀取器的寬度比寫入器窄4-5倍。 例如，現(xiàn)代驅(qū)動器中的寫入器寬度為50 μm，讀取器為10 μm。 但是，如何記錄比作者窄的曲目？ 如果磁頭寫了一個磁道，然后在磁道上添加了另一個磁道，但偏移量等于讀取器的寬度，則這兩個磁道都是可讀的。 結(jié)果，記錄過程將有點類似于屋頂上的瓦片排列：首先是第一行，然后將下一行以偏移量稍稍放下。 因此，基于效果的磁記錄方法的名稱。
The Shingled Magnetic Recording (SMR) technology increases the number of tracks per platter by 25%. A higher density is achieved by the use of a reader in a magnetic head, which is 4-5 times narrower than a writer. For instance, the writer in modern drives is 50 μm wide, the reader is 10 μm. But how does it record a track that is narrower than the writer? If the magnetic head writes a track and then adds another one on top of it, but with an offset equal to the reader width, then both tracks will be readable. As a result, the recording process will somewhat resemble tile arrangement on a rooftop: the top row first, then the next row is laid slightly lower with the offset. Hence the name of the magnetic recording method based on the effect.
上圖展示了7條帶狀軌道的外觀以及它們是如何產(chǎn)生的。
The figure above demonstrates the appearance of 7 shingled tracks and how they are produced.
首先，驅(qū)動器寫入磁道1。然后以等于讀取器寬度的偏移量寫入磁道2。 驅(qū)動器以這種方式繼續(xù)進行，直到寫入磁道8，形成磁道7和常規(guī)經(jīng)典磁道8。
First, the drive writes track 1. Then track 2 is written at an offset equal to the reader width. The drive proceeds in this manner until it writes track 8, which forms shingled track 7 and a regular classic track 8.
現(xiàn)在，您可能會問：如果讀取器的體積小5倍，而記錄的密度卻高5倍，為什么實際密度僅增加25％？ 實際上，磁頭定位系統(tǒng)的當(dāng)前精度為+/- 7 μm。 這一事實防止了形成小于35 μm的軌道。
Now, you may ask: why is the real density increase only 25% if the reader is 5 times smaller enabling recording 5 times denser? Actually, the current precision of the head positioning system is +/-7 μm. This fact prevents the creation of a track narrower than 35 μm.
疊瓦式磁性記錄的密度增加帶來了代價。 實現(xiàn)更高容量的能力在表面上強加了相當(dāng)復(fù)雜的數(shù)據(jù)排列。 該要求有一個明確的理由：要重寫單個數(shù)據(jù)扇區(qū)，不僅必須重寫具有該扇區(qū)的磁道，還必須重寫其后的所有磁道。
The increased density of shingled recording comes with a price. The ability to achieve higher capacity imposes considerable sophistication of data arrangement on the surface. The requirement has a solid reason: to rewrite a single data sector, you have to rewrite not just the track with that sector but also all the tracks that follow it.
當(dāng)然，要在任何地方重寫數(shù)據(jù)，必須先從該位置讀取數(shù)據(jù)。 因此，如果整個驅(qū)動器排列在帶狀的磁道中，則對單個位進行修改將需要從該位的位置到磁盤空間末端讀取和寫入所有磁道。 因此，書寫性能將下降極大的因素（數(shù)十萬次）。 顯然，沒有辦法完全避免寫入性能的下降。 但是有什么辦法可以加速它嗎？
Of course, to rewrite data anywhere, you have to read it from that location first. Thus, if the entire drive is arranged in shingled tracks, the modification of a single bit will require reading and writing of all the tracks from the bit’s location until the end of disk space. Consequently, the writing performance will drop by a huge factor (hundreds of thousands of times). Obviously, there is no way to avoid a decrease in writing performance altogether. But is there any way to accelerate it?
有。 為此，將SMR磁道合并為較小的組，稱為頻帶，因此僅將每個頻帶內(nèi)的磁道都混在一起。 每當(dāng)需要修改數(shù)據(jù)時，磁道的這種分組都允許僅讀取和重寫有限數(shù)量的磁道，而不是讀取整個磁盤，并且此細節(jié)大大加快了處理速度。
There is. And to do that SMR tracks are combined in smaller groups referred to as bands and therefore only tracks within every band are shingled. Whenever data needs to be modified, such grouping of the tracks allows to read and rewrite just a limited number of tracks instead of the entire platter, and this detail speeds up the process considerably.
但是，當(dāng)操作系統(tǒng)請求對100個扇區(qū)中的數(shù)據(jù)進行修改時，會發(fā)生什么情況（不幸的是，這些扇區(qū)位于不同的頻段內(nèi)）？ 顯然，驅(qū)動器將再次耗費幾乎所有時間來處理請求，并且如果在完成之前關(guān)閉電源，則數(shù)據(jù)將不太可能保持可訪問性和完整性。 為了避免這種情況，針對每種驅(qū)動器類型，考慮其應(yīng)用范圍，設(shè)計了特定的帶寬和記錄緩沖系統(tǒng)
But what happens when the operating system requests data modification in 100 sectors, which are unfortunately located within different bands? Clearly, the drive will again take almost an eternity to process the request and if a power shutdown occurs before it completes, the data will be very unlikely to remain accessible and intact. As an attempt to avoid such scenarios, specific band size and recording buffering system are designed for every drive type considering the area of their application.
可以識別三種支持混合記錄的設(shè)備：
Three main types of devices supporting shingled recording are recognized:
1) Drive Managed?驅(qū)動管理
2) Host Managed 主機管理
3) Host Aware. 主機應(yīng)答
類型2和類型3是在用于數(shù)據(jù)中心的特定設(shè)備中設(shè)計和運行的，它們不會在標準計算機上運行。 但是，類型1已被廣泛使用。 讓我們對其進行詳細描述。
Types 2 and 3 are designed and operated in specific equipment for data centers, they will not run in standard computers. However, type 1 is already widely used. Let us describe it in detail.
由驅(qū)動器管理的SMR驅(qū)動器不需要更改主機的BIOS或操作系統(tǒng)。 讀取/寫入過程的整個復(fù)雜性由驅(qū)動器本身的緩存系統(tǒng)處理。 存儲在這種驅(qū)動器上的數(shù)據(jù)的任何更改都首先在帶狀頻段之外的區(qū)域進行，并記錄在特殊的修改列表中，在西部數(shù)據(jù)公司中稱為輔助轉(zhuǎn)換器，在希捷中稱為媒體緩存。 這些修改稍后會在讀取時或在設(shè)備空閑時寫入帶狀頻段。 但是，當(dāng)連續(xù)執(zhí)行寫入操作時，驅(qū)動器最終會耗盡高速緩存空間，并在重新組合數(shù)據(jù)并將其寫入帶中時停止處理新請求一段時間。
Drive managed SMR drives do not require changes to the BIOS or operating system of the host computer. The entire complexity of the reading/writing processes is handled by the caching system of the drive itself. Any changes to the data stored on such a drive are first made in areas outside the shingled bands and registered in a special list of modifications referred to as the secondary translator in Western Digital and as media cache in Seagate models. These modifications are written to the shingled bands later while reading them, or when the device is idle. However, when writing is performed continuously, the drive eventually runs out of cache space and stops processing new requests for some time while reassembling data and writing it to the bands.
總結(jié)
To summarize.
SMR技術(shù)可以更合理地利用磁盤空間來增加硬盤容量。 將磁盤與SMR一起使用不需要對接口或驅(qū)動器的外形尺寸進行任何升級，因此，大多數(shù)用戶不會注意到向這項新技術(shù)的過渡。 缺點是與傳統(tǒng)的PMR光盤相比，寫入速度的下降很小。 顯然，如果二級轉(zhuǎn)換器或媒體緩存表丟失，這種HDD操作算法不會提高其可靠性，并使數(shù)據(jù)恢復(fù)嚴重復(fù)雜化
SMR technology applies a more rational use of disk space to increase the capacity of a hard disk.? The use of disks with SMR does not require any upgrade of the interface or the form factor of the drives, so the transition to this new technology will go unnoticed by most of the users. The disadvantage is a small drop in write speed compared to traditional PMR discs. Evidently, such an algorithm of HDD operation does not improve its reliability and seriously complicates data recovery if the secondary translator or media cache tables get lost.
實際上，邏輯訪問（LBA）考慮了扇區(qū)的轉(zhuǎn)換并跳過了缺陷（隱藏在缺陷列表中）。
In practice, the logical access (LBA) takes into account the translation of sectors and skips defects (hidden in the defect lists).
SMR驅(qū)動器按頻段組寫入數(shù)據(jù)。 第二級翻譯器考慮了這一點，HDD FW顯示了文件和文件夾的良好結(jié)構(gòu)。 但是，如果第二個轉(zhuǎn)換器（SMR）損壞，我們將在所有扇區(qū)中將其設(shè)為零。
SMR drives write the data by groups of bands. The second-level translator takes this into account, and HDD FW displays the good structure of files and folders. But if the second translator (SMR) is damaged, we will get zeros in all sectors.
轉(zhuǎn)載請注明：成都千喜數(shù)據(jù)恢復(fù)中心 » 如何使用PC-3000恢復(fù)WD(西部數(shù)據(jù))SMR(疊瓦式磁性記錄)硬盤二級編譯器損壞的數(shù)據(jù)
