ZFS *file* backed zpool for snapshots… safe in production?
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Are there any disadvantages of single file vdev zpool other than absence of fault tolerance which make it dangerous or impractical for production use?
e.g performance or stability concerns?
The man page only warns of absence of fault tolerance:
file A regular file. The use of files as a backing store is strongly
discouraged. It is designed primarily for experimental purposes,
as the fault tolerance of a file is only as good as the file sys‐
tem of which it is a part. A file must be specified by a full
path.
My use case is for snapshoting a database on a Linux server before syncing it to an offsite backup-server which uses a real disk backed mirrored zpool. The only purpose of using ZFS on the database server is to gain fast atomic snapshots which vastly reduce the time the database has to remain locked.
My aim is to keep the setup for the database server as automated as possible. This is intended to be set up on top of standard VPS images, where re-partitioning the main volume cannot be easily automated, and adding extra block devices is wasteful in this case.
Alternatively is there a better way to allocate a portion of the underlying ext4 partition to a zpool without partitioning it or in a way which can be automated without the need to delve into a VPS manager?
linux zfs
asked Jan 4 at 18:47
Thomas BrierleyThomas Brierley
1133
add a comment |
Are there any disadvantages of single file vdev zpool other than absence of fault tolerance which make it dangerous or impractical for production use?
e.g performance or stability concerns?
The man page only warns of absence of fault tolerance:
file A regular file. The use of files as a backing store is strongly
discouraged. It is designed primarily for experimental purposes,
as the fault tolerance of a file is only as good as the file sys‐
tem of which it is a part. A file must be specified by a full
path.
My use case is for snapshoting a database on a Linux server before syncing it to an offsite backup-server which uses a real disk backed mirrored zpool. The only purpose of using ZFS on the database server is to gain fast atomic snapshots which vastly reduce the time the database has to remain locked.
My aim is to keep the setup for the database server as automated as possible. This is intended to be set up on top of standard VPS images, where re-partitioning the main volume cannot be easily automated, and adding extra block devices is wasteful in this case.
Alternatively is there a better way to allocate a portion of the underlying ext4 partition to a zpool without partitioning it or in a way which can be automated without the need to delve into a VPS manager?
linux zfs
asked Jan 4 at 18:47
Thomas BrierleyThomas Brierley
1133
Here are two possible better ways to do this: use LVM under ext4 to do the snapshottting (although LVM snapshots have a performance overhead for writes until you delete them, and I don’t know of a way to efficiently send just the changed data from and LVM snapshot like ZFS can do); or, better yet, just use ZFS for the whole server instead of just for the database files.
– Dan
Jan 5 at 18:42
add a comment |
Are there any disadvantages of single file vdev zpool other than absence of fault tolerance which make it dangerous or impractical for production use?
e.g performance or stability concerns?
The man page only warns of absence of fault tolerance:
file A regular file. The use of files as a backing store is strongly
discouraged. It is designed primarily for experimental purposes,
as the fault tolerance of a file is only as good as the file sys‐
tem of which it is a part. A file must be specified by a full
path.
My use case is for snapshoting a database on a Linux server before syncing it to an offsite backup-server which uses a real disk backed mirrored zpool. The only purpose of using ZFS on the database server is to gain fast atomic snapshots which vastly reduce the time the database has to remain locked.
My aim is to keep the setup for the database server as automated as possible. This is intended to be set up on top of standard VPS images, where re-partitioning the main volume cannot be easily automated, and adding extra block devices is wasteful in this case.
Alternatively is there a better way to allocate a portion of the underlying ext4 partition to a zpool without partitioning it or in a way which can be automated without the need to delve into a VPS manager?
linux zfs
asked Jan 4 at 18:47
Thomas BrierleyThomas Brierley
1133
Are there any disadvantages of single file vdev zpool other than absence of fault tolerance which make it dangerous or impractical for production use?
e.g performance or stability concerns?
The man page only warns of absence of fault tolerance:
file A regular file. The use of files as a backing store is strongly
discouraged. It is designed primarily for experimental purposes,
as the fault tolerance of a file is only as good as the file sys‐
tem of which it is a part. A file must be specified by a full
path.
My use case is for snapshoting a database on a Linux server before syncing it to an offsite backup-server which uses a real disk backed mirrored zpool. The only purpose of using ZFS on the database server is to gain fast atomic snapshots which vastly reduce the time the database has to remain locked.
My aim is to keep the setup for the database server as automated as possible. This is intended to be set up on top of standard VPS images, where re-partitioning the main volume cannot be easily automated, and adding extra block devices is wasteful in this case.
Alternatively is there a better way to allocate a portion of the underlying ext4 partition to a zpool without partitioning it or in a way which can be automated without the need to delve into a VPS manager?
linux zfs
linux zfs
asked Jan 4 at 18:47
Thomas BrierleyThomas Brierley
1133
asked Jan 4 at 18:47
Thomas BrierleyThomas Brierley
1133
edited Jan 4 at 19:11
Thomas Brierley
asked Jan 4 at 18:47
Thomas BrierleyThomas Brierley
1133
asked Jan 4 at 18:47
Thomas BrierleyThomas Brierley
1133
asked Jan 4 at 18:47
Thomas BrierleyThomas Brierley
1133
1133
Here are two possible better ways to do this: use LVM under ext4 to do the snapshottting (although LVM snapshots have a performance overhead for writes until you delete them, and I don’t know of a way to efficiently send just the changed data from and LVM snapshot like ZFS can do); or, better yet, just use ZFS for the whole server instead of just for the database files.
– Dan
Jan 5 at 18:42
add a comment |
Here are two possible better ways to do this: use LVM under ext4 to do the snapshottting (although LVM snapshots have a performance overhead for writes until you delete them, and I don’t know of a way to efficiently send just the changed data from and LVM snapshot like ZFS can do); or, better yet, just use ZFS for the whole server instead of just for the database files.
– Dan
Jan 5 at 18:42
Here are two possible better ways to do this: use LVM under ext4 to do the snapshottting (although LVM snapshots have a performance overhead for writes until you delete them, and I don’t know of a way to efficiently send just the changed data from and LVM snapshot like ZFS can do); or, better yet, just use ZFS for the whole server instead of just for the database files.
– Dan
Jan 5 at 18:42
Here are two possible better ways to do this: use LVM under ext4 to do the snapshottting (although LVM snapshots have a performance overhead for writes until you delete them, and I don’t know of a way to efficiently send just the changed data from and LVM snapshot like ZFS can do); or, better yet, just use ZFS for the whole server instead of just for the database files.
– Dan
Jan 5 at 18:42
add a comment |
1 Answer
1
active
oldest
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ZFS is perfectly happy using a single file for a pool. You may not be, however. There are a few disadvantages.
- Performance. All ZFS iops are now translated to vnode ops, so ZFS is now sitting on top of a few more layers than it's used to. This comes with a significant performance impact.
- Reliability. ZFS ensures the atomicity of its transactions by writing its root node, called the "uberblock", with a single I/O issued to the uberblock's 4 locations. ZFS issues an fsync on the file after writing the uberblocks, but that turns out to be not 100% reliable.
- Redundancy. A single file (or a single disk for that matter) means that one of ZFS's better features, repairing read errors on the fly, is turned off. You may want to consider using a pair of files in a RAID1 (ZFS "mirror") config just to be a bit safer.
answered Jan 4 at 20:00
mmusantemmusante
60736
Thanks, #1 and #2 are the answer I was looking for (i.e significant performance and reliability reduction), I suspected there was more to it than mere absence of fault tolerance but wanted to be sure it was necessary to look for other options.
– Thomas Brierley
Jan 4 at 20:17
add a comment |
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1 Answer
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active
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1 Answer
1
active
oldest
votes
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votes
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oldest
votes
ZFS is perfectly happy using a single file for a pool. You may not be, however. There are a few disadvantages.
- Performance. All ZFS iops are now translated to vnode ops, so ZFS is now sitting on top of a few more layers than it's used to. This comes with a significant performance impact.
- Reliability. ZFS ensures the atomicity of its transactions by writing its root node, called the "uberblock", with a single I/O issued to the uberblock's 4 locations. ZFS issues an fsync on the file after writing the uberblocks, but that turns out to be not 100% reliable.
- Redundancy. A single file (or a single disk for that matter) means that one of ZFS's better features, repairing read errors on the fly, is turned off. You may want to consider using a pair of files in a RAID1 (ZFS "mirror") config just to be a bit safer.
answered Jan 4 at 20:00
mmusantemmusante
60736
Thanks, #1 and #2 are the answer I was looking for (i.e significant performance and reliability reduction), I suspected there was more to it than mere absence of fault tolerance but wanted to be sure it was necessary to look for other options.
– Thomas Brierley
Jan 4 at 20:17
add a comment |
ZFS is perfectly happy using a single file for a pool. You may not be, however. There are a few disadvantages.
- Performance. All ZFS iops are now translated to vnode ops, so ZFS is now sitting on top of a few more layers than it's used to. This comes with a significant performance impact.
- Reliability. ZFS ensures the atomicity of its transactions by writing its root node, called the "uberblock", with a single I/O issued to the uberblock's 4 locations. ZFS issues an fsync on the file after writing the uberblocks, but that turns out to be not 100% reliable.
- Redundancy. A single file (or a single disk for that matter) means that one of ZFS's better features, repairing read errors on the fly, is turned off. You may want to consider using a pair of files in a RAID1 (ZFS "mirror") config just to be a bit safer.
answered Jan 4 at 20:00
mmusantemmusante
60736
Thanks, #1 and #2 are the answer I was looking for (i.e significant performance and reliability reduction), I suspected there was more to it than mere absence of fault tolerance but wanted to be sure it was necessary to look for other options.
– Thomas Brierley
Jan 4 at 20:17
add a comment |
ZFS is perfectly happy using a single file for a pool. You may not be, however. There are a few disadvantages.
- Performance. All ZFS iops are now translated to vnode ops, so ZFS is now sitting on top of a few more layers than it's used to. This comes with a significant performance impact.
- Reliability. ZFS ensures the atomicity of its transactions by writing its root node, called the "uberblock", with a single I/O issued to the uberblock's 4 locations. ZFS issues an fsync on the file after writing the uberblocks, but that turns out to be not 100% reliable.
- Redundancy. A single file (or a single disk for that matter) means that one of ZFS's better features, repairing read errors on the fly, is turned off. You may want to consider using a pair of files in a RAID1 (ZFS "mirror") config just to be a bit safer.
answered Jan 4 at 20:00
mmusantemmusante
60736
ZFS is perfectly happy using a single file for a pool. You may not be, however. There are a few disadvantages.
- Performance. All ZFS iops are now translated to vnode ops, so ZFS is now sitting on top of a few more layers than it's used to. This comes with a significant performance impact.
- Reliability. ZFS ensures the atomicity of its transactions by writing its root node, called the "uberblock", with a single I/O issued to the uberblock's 4 locations. ZFS issues an fsync on the file after writing the uberblocks, but that turns out to be not 100% reliable.
- Redundancy. A single file (or a single disk for that matter) means that one of ZFS's better features, repairing read errors on the fly, is turned off. You may want to consider using a pair of files in a RAID1 (ZFS "mirror") config just to be a bit safer.
answered Jan 4 at 20:00
mmusantemmusante
60736
answered Jan 4 at 20:00
mmusantemmusante
60736
answered Jan 4 at 20:00
mmusantemmusante
60736
answered Jan 4 at 20:00
mmusantemmusante
60736
60736
Thanks, #1 and #2 are the answer I was looking for (i.e significant performance and reliability reduction), I suspected there was more to it than mere absence of fault tolerance but wanted to be sure it was necessary to look for other options.
– Thomas Brierley
Jan 4 at 20:17
add a comment |
Thanks, #1 and #2 are the answer I was looking for (i.e significant performance and reliability reduction), I suspected there was more to it than mere absence of fault tolerance but wanted to be sure it was necessary to look for other options.
– Thomas Brierley
Jan 4 at 20:17
Thanks, #1 and #2 are the answer I was looking for (i.e significant performance and reliability reduction), I suspected there was more to it than mere absence of fault tolerance but wanted to be sure it was necessary to look for other options.
– Thomas Brierley
Jan 4 at 20:17
Thanks, #1 and #2 are the answer I was looking for (i.e significant performance and reliability reduction), I suspected there was more to it than mere absence of fault tolerance but wanted to be sure it was necessary to look for other options.
– Thomas Brierley
Jan 4 at 20:17
add a comment |
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Here are two possible better ways to do this: use LVM under ext4 to do the snapshottting (although LVM snapshots have a performance overhead for writes until you delete them, and I don’t know of a way to efficiently send just the changed data from and LVM snapshot like ZFS can do); or, better yet, just use ZFS for the whole server instead of just for the database files.
– Dan
Jan 5 at 18:42