6 ms·

The biggest players in the game do not use SSDs for persistent storage longer than x weeks. It is offloaded to tape at some point and restored periodically.

vegardx 6y ago
Uhm, what? There are tons of ways to prevent data loss, none of them involves writing the data out to tapes and then back in again.
- sushshshsh 6y ago
  Sure, you can also write to disk or other media. But are you trying to argue that certain large companies don't use tape?
  - vegardx 6y ago
    I never said that. There's simply no good reason to periodically write your data from flash to $other every now and them, and then back to flash. There are heaps of other ways to prevent data loss or performance degradation in flash storage. There are methods like tiered storage, where only the most active data is present in Flash-storage, much like write back caching.
  - deleted 6y ago
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deleted 6y ago
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gruez 6y ago
>It is offloaded to tape at some point and restored periodically. This makes no sense. The main problem with disabling write flushing is what happens if the OS crashes or the power goes out. Doing periodic backups/restores provides a "last known good state" to revert to, but you'll still lose all the writes between the last backup and when you crashed. Depending on your workload this might be fine, but I doubt the COO is going to be pleased when he finds out you lost all customer orders from today. The bit about "restoring periodically" also doesn't make any sense because such events are easily detectable. There's no need to constantly take the system offline to do a restore. Disabling write flushing isn't going to cause increased bitrot.
- duskwuff 6y ago
  Explicitly rewriting data periodically might make sense if you're really paranoid about flash fading over time. But bouncing the data through tape (tape!!) still makes no sense; the sensible way of managing this would be to mirror the data directly to another SSD.
  - sushshshsh 6y ago
    We are arguing about nothing. Live data (being accessed many times per day) stays on SSDs. The middle tier of data is a gray area and can go on SSDs or disk. But if you think that your FB or Youtube or Fidelity or Geico or SSN or IRS or Apple or Google data isn't sitting on a tape somewhere, you are extremely mistaken, because I was the one who wrote the tape control software they purchased from us.
    - wtallis 6y ago
      Nobody's denying that the data makes it to tape eventually. What everyone finds hard to believe is your assertion that data is ever moved from tape back into warm storage during the ordinary course of business. Enterprises use tape for backup. They only read data off tapes after something goes very wrong, or periodically to verify that their backup process is actually working. But except after a catastrophe, data read from tape is not routinely used to re-populate warm storage.
      - sushshshsh 6y ago
        The Library of Congress does exactly what you've described every day. A researcher desires to download a 50 minute archived video. A request is sent from their laptop to a lookup table server. The lookup table contains the metadata for where that file is stored. Then the request is passed to a media server which has an SSD and RAM large enough for receiving the actual media file. It opens a connection with the tape library. The tape library handles loading the media from tape to a staging server, which also has an SSD. So totally the media file goes from tape, to staging SSD via hardwire, to main server's SSD over the network, to client's device over the network.
motives 6y ago
I'm also curious as to whether this is true. From what I understand and can gather from tech talks from large firms, it is common (up to and beyond petabyte scale) to use ceph clusters purely consisting of SSDs and HDDs (no tape) to store mission critical data, with cache tiering used to balance hot and cold data. AFAIK, because of their self-healing nature thanks to replication/erasure coding algorithms, all that needs to be done is replace corrupted drives periodically, thus making tape drives non-essential unless periodic full backups are required for off-site storage. Please feel free to correct me if I'm wrong in any of this. Thanks.
- nix23 6y ago
  >to use ceph clusters purely Exactly! Use ceph so you don't have to care about burning ssd/hdd/server/switch/racks/dc, you have your object-storeage, FS, block-device, with one service and that's it.
saagarjha 6y ago
They use tape because they have insanely large amounts of data they want to store and no need to have fast access to them, not because they are a good replacement for SSDs.

vegardx 6y ago

Uhm, what? There are tons of ways to prevent data loss, none of them involves writing the data out to tapes and then back in again.

sushshshsh 6y ago
Sure, you can also write to disk or other media. But are you trying to argue that certain large companies don't use tape?
- vegardx 6y ago
  I never said that. There's simply no good reason to periodically write your data from flash to $other every now and them, and then back to flash. There are heaps of other ways to prevent data loss or performance degradation in flash storage. There are methods like tiered storage, where only the most active data is present in Flash-storage, much like write back caching.
- deleted 6y ago
  [deleted]

deleted 6y ago

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gruez 6y ago

>It is offloaded to tape at some point and restored periodically. This makes no sense. The main problem with disabling write flushing is what happens if the OS crashes or the power goes out. Doing periodic backups/restores provides a "last known good state" to revert to, but you'll still lose all the writes between the last backup and when you crashed. Depending on your workload this might be fine, but I doubt the COO is going to be pleased when he finds out you lost all customer orders from today. The bit about "restoring periodically" also doesn't make any sense because such events are easily detectable. There's no need to constantly take the system offline to do a restore. Disabling write flushing isn't going to cause increased bitrot.

duskwuff 6y ago
Explicitly rewriting data periodically might make sense if you're really paranoid about flash fading over time. But bouncing the data through tape (tape!!) still makes no sense; the sensible way of managing this would be to mirror the data directly to another SSD.
- sushshshsh 6y ago
  We are arguing about nothing. Live data (being accessed many times per day) stays on SSDs. The middle tier of data is a gray area and can go on SSDs or disk. But if you think that your FB or Youtube or Fidelity or Geico or SSN or IRS or Apple or Google data isn't sitting on a tape somewhere, you are extremely mistaken, because I was the one who wrote the tape control software they purchased from us.
  - wtallis 6y ago
    Nobody's denying that the data makes it to tape eventually. What everyone finds hard to believe is your assertion that data is ever moved from tape back into warm storage during the ordinary course of business. Enterprises use tape for backup. They only read data off tapes after something goes very wrong, or periodically to verify that their backup process is actually working. But except after a catastrophe, data read from tape is not routinely used to re-populate warm storage.
    - sushshshsh 6y ago
      The Library of Congress does exactly what you've described every day. A researcher desires to download a 50 minute archived video. A request is sent from their laptop to a lookup table server. The lookup table contains the metadata for where that file is stored. Then the request is passed to a media server which has an SSD and RAM large enough for receiving the actual media file. It opens a connection with the tape library. The tape library handles loading the media from tape to a staging server, which also has an SSD. So totally the media file goes from tape, to staging SSD via hardwire, to main server's SSD over the network, to client's device over the network.

motives 6y ago

I'm also curious as to whether this is true. From what I understand and can gather from tech talks from large firms, it is common (up to and beyond petabyte scale) to use ceph clusters purely consisting of SSDs and HDDs (no tape) to store mission critical data, with cache tiering used to balance hot and cold data. AFAIK, because of their self-healing nature thanks to replication/erasure coding algorithms, all that needs to be done is replace corrupted drives periodically, thus making tape drives non-essential unless periodic full backups are required for off-site storage. Please feel free to correct me if I'm wrong in any of this. Thanks.

nix23 6y ago
>to use ceph clusters purely Exactly! Use ceph so you don't have to care about burning ssd/hdd/server/switch/racks/dc, you have your object-storeage, FS, block-device, with one service and that's it.

saagarjha 6y ago

They use tape because they have insanely large amounts of data they want to store and no need to have fast access to them, not because they are a good replacement for SSDs.