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Toshiba L200

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On 12/27/2018 at 7:10 PM, Cuttysark said:

Toshiba L200 are all PMR, they use this media:

 http://www.sdk.co.jp/english/news/2017/26793.html

SMR is not a feature of the magnetic platter, but of the write head. The data on the media is always stored using PMR. It can be read back at full speed without going through any special processing.

But once the areal density of those 1TB-2.5" platters is too high for the L200's write head to write a single track without overwriting neighboring tracks, it has to write using SMR. And that's exactly what the L200 drives with 128 MB RAM buffer do.

To differentiate SMR drives from faster drives, the ones which can still write single tracks / sectors randomly, the latter are now called CMR (Conventional Magnetic Recording) drives. The L200 models with an 8 MB buffer are CMR drives.

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On 1/21/2019 at 3:01 AM, jtsn said:

SMR is not a feature of the magnetic platter, but of the write head. The data on the media is always stored using PMR. It can be read back at full speed without going through any special processing.

But once the areal density of those 1TB-2.5" platters is too high for the L200's write head to write a single track without overwriting neighboring tracks, it has to write using SMR. And that's exactly what the L200 drives with 128 MB RAM buffer do.

To differentiate SMR drives from faster drives, the ones which can still write single tracks / sectors randomly, the latter are now called CMR (Conventional Magnetic Recording) drives. The L200 models with an 8 MB buffer are CMR drives.

Doesn't the inconsistent performance of SMR only matter if you're going to be doing a lot of erasing and rewriting like you might do with a RAID setup? SMR drives would be intolerable in that application. If you only plan to write something to your drive once then leave it there pretty much forever it shouldn't be as big of a deal, right? 

Edited by OldComputerGuy
Typos

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. If you only plan to write something to your drive once then leave it there pretty much forever it shouldn't be as big of a deal, right? 

Correct. Although keep in mind even a single write large enough may cause you to see the performance hit.

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On 1/21/2019 at 8:01 AM, jtsn said:

SMR is not a feature of the magnetic platter, but of the write head. The data on the media is always stored using PMR. It can be read back at full speed without going through any special processing.

But once the areal density of those 1TB-2.5" platters is too high for the L200's write head to write a single track without overwriting neighboring tracks, it has to write using SMR. And that's exactly what the L200 drives with 128 MB RAM buffer do.

To differentiate SMR drives from faster drives, the ones which can still write single tracks / sectors randomly, the latter are now called CMR (Conventional Magnetic Recording) drives. The L200 models with an 8 MB buffer are CMR drives.

Sorry for the late reply, but yes, you were right, these disks are definitely SMR, I have a few of them and it's especially noticeable on a btrfs raid5 pool, writes start fast enough but after a few GB transfer speed tanks.

Turns out I had a cable problem with one of the disks, so the performance issues might be related to that, let me test some more and I'll post an update later.

Edited by Cuttysark

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Cable problem is fixed and still bad sustained write performance, so I have no doubts now that they are SMR, even as single drive write performance decreases after a while but like mentioned it's much more noticeable in a raid config, I have a 4 disk raid5 btrfs pool with theses disks, and transferring a large number of large video files (from a fast SSD pool) speed starts at around 300MB/s which is about what I expected, but after about 30 or 40GB transferred (maybe they have a small CMR zone?) it tanks to around 30MB/s and stays like that for the duration, I have other raid pools with CMR disks and transfer speeds remain consistent for the whole tranfer.

 

259838688_Screenshot2019-08-1719_38_38.png.51ad137aeaa4f2af5f10d89c8ee63b79.png

 

 

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