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Physical and logical extents size

Does swap need to be on a contiguous LVM logical volumeHow to correct fs size for logical volumeWhat is the proper way to shrink a LVM partition?Why are there two different values for the size of a drive and how to reconcile them with device-mapper and LVM?Move logical volume to a new physical diskHow to resize logical volume in Red Hat LinuxMove all data in LV to first PV, remove othersHow to shrink a physical volume?LVM Shrink to remove a deviceSetting up RAID1 with an active physical volume (Debian 9 stretch)

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty{ margin-bottom:0;
}

3

1

I have created a partition with 36TB (/dev/sdb1) in rhel 6.6.
Now I want use this for LVM.

• What is recommended size for Physical Extents, Volume Extents and Logical Extents?


• How important PE, VE and LE size to define while creating?

I want to create LV size of 10TB, 10TB, 6TB.
I am using for file sharing through NFS and samba. Performance should be good. Please guide me for this...

linux performance lvm

share|improve this question

edited 8 hours ago

Alexey Vazhnov

1966 bronze badges

asked May 15 '15 at 4:05

sagarsagar

6911 gold badge11 silver badge55 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  The answers to your questions are available in plenty of the docs available. Did you try googling?
  
  – Sree
  May 15 '15 at 4:19
  

  
  
  
  

add a comment | 

3

1

I have created a partition with 36TB (/dev/sdb1) in rhel 6.6.
Now I want use this for LVM.

• What is recommended size for Physical Extents, Volume Extents and Logical Extents?


• How important PE, VE and LE size to define while creating?

I want to create LV size of 10TB, 10TB, 6TB.
I am using for file sharing through NFS and samba. Performance should be good. Please guide me for this...

linux performance lvm

share|improve this question

edited 8 hours ago

Alexey Vazhnov

1966 bronze badges

asked May 15 '15 at 4:05

sagarsagar

6911 gold badge11 silver badge55 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  The answers to your questions are available in plenty of the docs available. Did you try googling?
  
  – Sree
  May 15 '15 at 4:19
  

  
  
  
  

add a comment | 

I have created a partition with 36TB (/dev/sdb1) in rhel 6.6.
Now I want use this for LVM.

• What is recommended size for Physical Extents, Volume Extents and Logical Extents?


• How important PE, VE and LE size to define while creating?

I want to create LV size of 10TB, 10TB, 6TB.
I am using for file sharing through NFS and samba. Performance should be good. Please guide me for this...

linux performance lvm

share|improve this question

edited 8 hours ago

Alexey Vazhnov

1966 bronze badges

asked May 15 '15 at 4:05

sagarsagar

6911 gold badge11 silver badge55 bronze badges

share|improve this question

edited 8 hours ago

Alexey Vazhnov

1966 bronze badges

asked May 15 '15 at 4:05

sagarsagar

6911 gold badge11 silver badge55 bronze badges

share|improve this question

edited 8 hours ago

Alexey Vazhnov

1966 bronze badges

asked May 15 '15 at 4:05

sagarsagar

6911 gold badge11 silver badge55 bronze badges

edited 8 hours ago

Alexey Vazhnov

1966 bronze badges

edited 8 hours ago

Alexey Vazhnov

1966 bronze badges

asked May 15 '15 at 4:05

sagarsagar

6911 gold badge11 silver badge55 bronze badges

asked May 15 '15 at 4:05

sagarsagar

6911 gold badge11 silver badge55 bronze badges

1 Answer
1

active

oldest

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6

First off, you're confused about what some of those are. You can set the physical extent size with a fair bit of flexibility (vgcreate -s <size-of-PE>). But it doesn't matter, you should just go with the default. To quote the manpage:

The default is 4 MiB.… [H]aving a large number of extents will slow down the tools but have no impact on I/O performance to the logical volume.

When they say "no impact on I/O performance", they mean that literally. LVM is a wrapper around device-mapper and the LVM tools do not expose the physical extent size to device-mapper. The actual kernel code doing the I/O is unaware of the extent size. So it doesn't matter, unless you need to run lvcreate (etc.) all the time as part of your workload.

(Note it can influence data alignment; see below.)

The size in logical extents (set with lvcreate -l «number-of-extents») is just a way to specify the size of the logical volume. LV size = physical extent size * number of extents. Generally though you'd use -L «size» because that does the math for you, and let's you specify human-friendly sizes like 10T

I'm not sure what you mean by "volume extents", unless you mean the same as the above. Or maybe you mean the length of a physical volume in extents, but that'd also just be another way to specify the size.

What you should care about

At 36TB, your sdb is very unlikely to be a plain old disk. You should find out its alignment requirements and make sure you get everything aligned correctly. This is easiest if data_alignment_offset_detection (see man 5 lvm.conf) works in your setup—then the LVM tools will handle this all for you. Allocation (of a logical volume) is done in entire physical extent chunks, so you probably want the PE size to be a multiple of your alignment size. But at 4MiB, it probably already is. Misalignment will kill I/O performance, especially of writes.

You should also ensure that you're using an appropriate RAID level for your workload. Consider also battery-backed cache.

share|improve this answer

edited Apr 13 '16 at 13:51

dr01

17.5k1111 gold badges5656 silver badges7979 bronze badges

answered May 15 '15 at 6:00

derobertderobert

79k88 gold badges175175 silver badges231231 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Hi, We are using Hardware RAID 6 and I am planing to create 9TB x 4 partitions. /dev/sdb1/2/3/4 and create lvm with striping and I also use 64MB PE for better performance. Is this fine ?
  
  – sagar
  May 15 '15 at 8:26
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @sagar I'm not sure why you'd slice the disk into multiple pieces inside the kernel (by partitioning) only to put it back together inside the kernel (via LVM). Just do the straightforward thing—one large partition, put a PV on it, slice it with LVM.
  
  – derobert
  May 15 '15 at 21:27
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Hi derobert, what is the Max size we can create lv In lvm2 for default PE 4 MB
  
  – sagar
  May 16 '15 at 22:19
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @sagar LVM2 metadata is text-based; it doesn't have fixed-width binary numbers. The limits come from the kernel's ability to parse the numbers. On a 64-bit kernel, the limit is in the multiple-exabyte range.
  
  – derobert
  May 16 '15 at 23:40
  

  
  
  
  

add a comment | 

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6

First off, you're confused about what some of those are. You can set the physical extent size with a fair bit of flexibility (vgcreate -s <size-of-PE>). But it doesn't matter, you should just go with the default. To quote the manpage:

The default is 4 MiB.… [H]aving a large number of extents will slow down the tools but have no impact on I/O performance to the logical volume.

When they say "no impact on I/O performance", they mean that literally. LVM is a wrapper around device-mapper and the LVM tools do not expose the physical extent size to device-mapper. The actual kernel code doing the I/O is unaware of the extent size. So it doesn't matter, unless you need to run lvcreate (etc.) all the time as part of your workload.

(Note it can influence data alignment; see below.)

The size in logical extents (set with lvcreate -l «number-of-extents») is just a way to specify the size of the logical volume. LV size = physical extent size * number of extents. Generally though you'd use -L «size» because that does the math for you, and let's you specify human-friendly sizes like 10T

I'm not sure what you mean by "volume extents", unless you mean the same as the above. Or maybe you mean the length of a physical volume in extents, but that'd also just be another way to specify the size.

What you should care about

At 36TB, your sdb is very unlikely to be a plain old disk. You should find out its alignment requirements and make sure you get everything aligned correctly. This is easiest if data_alignment_offset_detection (see man 5 lvm.conf) works in your setup—then the LVM tools will handle this all for you. Allocation (of a logical volume) is done in entire physical extent chunks, so you probably want the PE size to be a multiple of your alignment size. But at 4MiB, it probably already is. Misalignment will kill I/O performance, especially of writes.

You should also ensure that you're using an appropriate RAID level for your workload. Consider also battery-backed cache.

share|improve this answer

edited Apr 13 '16 at 13:51

dr01

17.5k1111 gold badges5656 silver badges7979 bronze badges

answered May 15 '15 at 6:00

derobertderobert

79k88 gold badges175175 silver badges231231 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Hi, We are using Hardware RAID 6 and I am planing to create 9TB x 4 partitions. /dev/sdb1/2/3/4 and create lvm with striping and I also use 64MB PE for better performance. Is this fine ?
  
  – sagar
  May 15 '15 at 8:26
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @sagar I'm not sure why you'd slice the disk into multiple pieces inside the kernel (by partitioning) only to put it back together inside the kernel (via LVM). Just do the straightforward thing—one large partition, put a PV on it, slice it with LVM.
  
  – derobert
  May 15 '15 at 21:27
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Hi derobert, what is the Max size we can create lv In lvm2 for default PE 4 MB
  
  – sagar
  May 16 '15 at 22:19
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @sagar LVM2 metadata is text-based; it doesn't have fixed-width binary numbers. The limits come from the kernel's ability to parse the numbers. On a 64-bit kernel, the limit is in the multiple-exabyte range.
  
  – derobert
  May 16 '15 at 23:40
  

  
  
  
  

add a comment | 

6

First off, you're confused about what some of those are. You can set the physical extent size with a fair bit of flexibility (vgcreate -s <size-of-PE>). But it doesn't matter, you should just go with the default. To quote the manpage:

The default is 4 MiB.… [H]aving a large number of extents will slow down the tools but have no impact on I/O performance to the logical volume.

When they say "no impact on I/O performance", they mean that literally. LVM is a wrapper around device-mapper and the LVM tools do not expose the physical extent size to device-mapper. The actual kernel code doing the I/O is unaware of the extent size. So it doesn't matter, unless you need to run lvcreate (etc.) all the time as part of your workload.

(Note it can influence data alignment; see below.)

The size in logical extents (set with lvcreate -l «number-of-extents») is just a way to specify the size of the logical volume. LV size = physical extent size * number of extents. Generally though you'd use -L «size» because that does the math for you, and let's you specify human-friendly sizes like 10T

I'm not sure what you mean by "volume extents", unless you mean the same as the above. Or maybe you mean the length of a physical volume in extents, but that'd also just be another way to specify the size.

What you should care about

At 36TB, your sdb is very unlikely to be a plain old disk. You should find out its alignment requirements and make sure you get everything aligned correctly. This is easiest if data_alignment_offset_detection (see man 5 lvm.conf) works in your setup—then the LVM tools will handle this all for you. Allocation (of a logical volume) is done in entire physical extent chunks, so you probably want the PE size to be a multiple of your alignment size. But at 4MiB, it probably already is. Misalignment will kill I/O performance, especially of writes.

You should also ensure that you're using an appropriate RAID level for your workload. Consider also battery-backed cache.

share|improve this answer

edited Apr 13 '16 at 13:51

dr01

17.5k1111 gold badges5656 silver badges7979 bronze badges

answered May 15 '15 at 6:00

derobertderobert

79k88 gold badges175175 silver badges231231 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Hi, We are using Hardware RAID 6 and I am planing to create 9TB x 4 partitions. /dev/sdb1/2/3/4 and create lvm with striping and I also use 64MB PE for better performance. Is this fine ?
  
  – sagar
  May 15 '15 at 8:26
  
  
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @sagar I'm not sure why you'd slice the disk into multiple pieces inside the kernel (by partitioning) only to put it back together inside the kernel (via LVM). Just do the straightforward thing—one large partition, put a PV on it, slice it with LVM.
  
  – derobert
  May 15 '15 at 21:27
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Hi derobert, what is the Max size we can create lv In lvm2 for default PE 4 MB
  
  – sagar
  May 16 '15 at 22:19
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @sagar LVM2 metadata is text-based; it doesn't have fixed-width binary numbers. The limits come from the kernel's ability to parse the numbers. On a 64-bit kernel, the limit is in the multiple-exabyte range.
  
  – derobert
  May 16 '15 at 23:40
  

  
  
  
  

add a comment | 

First off, you're confused about what some of those are. You can set the physical extent size with a fair bit of flexibility (vgcreate -s <size-of-PE>). But it doesn't matter, you should just go with the default. To quote the manpage:

The default is 4 MiB.… [H]aving a large number of extents will slow down the tools but have no impact on I/O performance to the logical volume.

When they say "no impact on I/O performance", they mean that literally. LVM is a wrapper around device-mapper and the LVM tools do not expose the physical extent size to device-mapper. The actual kernel code doing the I/O is unaware of the extent size. So it doesn't matter, unless you need to run lvcreate (etc.) all the time as part of your workload.

(Note it can influence data alignment; see below.)

The size in logical extents (set with lvcreate -l «number-of-extents») is just a way to specify the size of the logical volume. LV size = physical extent size * number of extents. Generally though you'd use -L «size» because that does the math for you, and let's you specify human-friendly sizes like 10T

I'm not sure what you mean by "volume extents", unless you mean the same as the above. Or maybe you mean the length of a physical volume in extents, but that'd also just be another way to specify the size.

What you should care about

At 36TB, your sdb is very unlikely to be a plain old disk. You should find out its alignment requirements and make sure you get everything aligned correctly. This is easiest if data_alignment_offset_detection (see man 5 lvm.conf) works in your setup—then the LVM tools will handle this all for you. Allocation (of a logical volume) is done in entire physical extent chunks, so you probably want the PE size to be a multiple of your alignment size. But at 4MiB, it probably already is. Misalignment will kill I/O performance, especially of writes.

You should also ensure that you're using an appropriate RAID level for your workload. Consider also battery-backed cache.

share|improve this answer

edited Apr 13 '16 at 13:51

dr01

17.5k1111 gold badges5656 silver badges7979 bronze badges

answered May 15 '15 at 6:00

derobertderobert

79k88 gold badges175175 silver badges231231 bronze badges

share|improve this answer

edited Apr 13 '16 at 13:51

dr01

17.5k1111 gold badges5656 silver badges7979 bronze badges

answered May 15 '15 at 6:00

derobertderobert

79k88 gold badges175175 silver badges231231 bronze badges

edited Apr 13 '16 at 13:51

dr01

17.5k1111 gold badges5656 silver badges7979 bronze badges

edited Apr 13 '16 at 13:51

dr01

17.5k1111 gold badges5656 silver badges7979 bronze badges

answered May 15 '15 at 6:00

derobertderobert

79k88 gold badges175175 silver badges231231 bronze badges

answered May 15 '15 at 6:00

derobertderobert

79k88 gold badges175175 silver badges231231 bronze badges