1. Are Hot Copies Readable and Writable?
Yes you can Read AND Write to your Hot Copy.
2. Does the FREE Hot Copy Come with Technical Support?
You may ask for help and report issues using our forums.
3. Does the Hot Copy Survive a Reboot?
NO. If you reboot you lose your Hot Copy(s). This is similar to LVM2 which does not support snapshots across reboots.
4. Does Hot Copy use LVM?
NO. Hot Copy does not use or depend on LVM in any way. This is a big advantage. You Do Not need LVM to use Hot Copy.
5. Can I take Multiple Hot Copies of the Same Device?
No. Yes as of Hot Copy 3.3.0 you can take multiple point-in-time snapshots of the same device. Be aware there is a performance penalty when you create multiple snapshots for the same device.
6. How do I allocate Space for my Hot Copy?
You don’t need to. Hot Copy will automatically use available free space on your disk to store the Hot Copy! It will only use as much space as needed to maintain the snapshot and will grow this space as you make changes to the real device or to the Hot Copy. You can override this and specify a different device to store the changed blocks on. You can also control a free space quota to prevent your drive from filling up.
7. What Kernel Versions are Supported?
Current Hot Copy supports 2.6 Linux kernels.
8. Why do I need Hot Copy? What’s wrong with LVM snapshots?
LVM is Great! We found LVM did not fit the need of many users so we created Hot Copy.
Here are some reasons LVM snapshots are not always best:
- LVM Snapshots perform poorly on busy servers (Hot Copy is more efficient and typically performs better than LVM Snapshots)
- You always need to have all of your data on LVM to use LVM snapshots! Many people have servers or are administrating servers that don’t use LVM. Or you may have some data on a Logical Volume while other data is on a partition. For example the root device is commonly Not on LVM.
- The LVM snapshot needs dedicated free space in the LVM volume group and normally all of this is already allocated to the existing Logical Volumes. No free space in your LVM Volume Group means No LVM snapshots.
- Your system must be upgraded to LVM2 to get writeable snapshots.
- You may need to patch LVM with the VFS-lock patch to get consistent file system snapshots.
9. How long does it take to create a Hot Copy?
The file system is only frozen for milliseconds and the entire operations completes in 1-2 seconds.
10. How Much Memory Does Hot Copy Use?
Hot Copy uses a temporary memory cache to hold "in flight" changed blocks before they are written to disk. This memory usage depends on how write intensive your server is. As long as your server is not already very low on physical memory before you create the hot copy you should not have a problem.
Hot Copy uses No memory intensive bitmaps and scales VERY well with large disks.
11. I have X number of Terabytes to Hot Copy. Can hcp handle that?
Yes. There are No known limits with Hot Copy
12. How Much Overhead Does Hot Copy Create?
To maintain the Snapshot Hot Copy uses the a very common copy-on-write method. Other examples of copy-on-write snapshots are: Linux LVM Snapshots and Microsoft Volume Shadow Copy.
After you create a Hot Copy snapshot the first time a disk block is overwritten with changes the Hot Copy device driver must save a backup copy of the block before the change is written to the disk. This means the first time a block is overwritten on disk after making the snapshot there is an extra read and write triggered for writes that overwrite existing disk blocks.
Hot Copy does use resources to maintain the point-in-time snapshot so its recommened you keep some unused resources available on your server. Most servers even VERY I/O intensive servers handle Hot Copy with great ease.
13. Is Hot Copy CDP?
NO. While CDP requires a snapshot. Hot Copy is not CDP. CDP requires a snapshot and near-Continuous block level change tracking or delta computation. Hot Copy will make a perfect point-in-time snapshot. It can NOT tell you what the deltas are since your last backup and it can NOT reduce your backup windows. Only R1Soft CDP can do that.
14. What File Systems Does Hot Copy work with?
Hot Copy is Not file system dependent. It is tested primarily on ext3 and should work well on any file system (note: it does Not work on Network File Systems).
15. Can I use Hot Copy on a Network File System like NFS or CIFS?
No. Hot Copy works at a low level and must have direct access to a block device.
16. Does Hot Copy Work with Journaled File Systems? How about synchronous I/O?
Yes and Yes. The Hot Copy device driver works in perfect harmony with Journaled file system and synchronous disk I/O. This is because Writes that require a copy-on-write operation to your real disk do not complete until the old data is read from disk and the new data is written through to disk (copy-on-write).
Note writes to the Snapshot (virtual disk) are not guaranteed to be synchronous.