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Is it safe to use an SD card as a permanent secondary storage for my laptop (by letting it be there, without removing it regularly)?
I don't know how SD card hardware is internally different from an SSD hard drive, and my question is: can an SD card handle many daily IO operations like a regular HDD? Can it work for a few years without being formatted?
Siavash Mortazavi
Posted 2016-05-08T21:31:49.780
Reputation: 13
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It might do for secondary storage, so long as you're not doing a great deal of editing on it, but I would keep a backup.
SD cards lack any of the intelligence that an SSD controller has and are effectively just a dumb block of flash memory.
SSDs have features like wear levelling that can prolong the life of the flash device by a great deal by preventing repeated rewrites on the same block in a short period of time.
SD cards do not have wear levelling and many filesystems will repeatedly rewrite the same blocks with minor changes every time a file changes. Unless you make the filesystem read-only (not practical with Windows) then you will quickly get a corrupt filesystem.
It might last a couple of years, or it might die after a few months. The quality of the card matters, as does the workload of the operating system and the filesystem.
Linux might fare better as you can use one of the alternate filesystems that are optimised for SD flash devices, but NTFS is not a particularly good filesystem for flash devices from what I've heard.
Mokubai
Posted 2016-05-08T21:31:49.780
Reputation: 64 434
SD cards have a microcontroller that does in fact do wear leveling. - http://www.bunniestudios.com/blog/?p=3554 - SD cards are slower primarily because they don't use the SATA bus.
– LawrenceC – 2016-05-08T23:45:31.397@LawrenceC much of what I can find suggests that wear levelling is not a mandatory part of the spec and that cheaper cards may not implement it at all. It seems you cannot guarantee that any given card will have this feature as there is no way to expose it to the host. Chances are that branded cards and industrial grade ones will do wear levelling, but I wouldn't be surprised if cheap "no name" ones do not or have a flawed implementation. This would explain my experience with "bad" SD cards. – Mokubai – 2016-05-09T06:04:28.817
You may be right ... No way to really know either without looking at the microcontroller firmware. – LawrenceC – 2016-05-09T10:02:31.177
Mokubai & LawrenceC, Thank you both for providing insights. I appreciate your time.and knowledge ;-) – Siavash Mortazavi – 2016-05-14T14:20:04.183