Before i consider purchasing an SSD or two please can someone answer these questions?
Is it one SSD drive per volume. (ie in read only mode, if I put an SSD in, can I used half of the SSD as a cache for voume1 and the other half for volume2 or can it not be split?
Second related question, is it automatically also used as a cache for volume0 or perhaps just used as a member of the raid 1 for volume0 as is the case for all other disks?
If it helps this is on a 5304T
Thanks
SSD Cache
Moderator: Lillian.W@AST
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chris.e
- Posts: 53
- Joined: Tue Jun 09, 2020 6:28 am
Re: SSD Cache
The answer is no, you can't.
It's one SSD per volume.
It's one SSD per volume.
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chris.e
- Posts: 53
- Joined: Tue Jun 09, 2020 6:28 am
Re: SSD Cache
I decided it was better to create a hybrid raid 1 array.
ie Using a matched size SSD and HDD you can create a RAID1 as normal but then using mdadm cli add a "writemostly" option to the HDD. This causes the kernel to read only from the SSD. ie massive read performance increase.
For example:
echo writemostly > /sys/block/md1/md/dev-sda4/state
Where sda is my HDD and volume1 is stored at md1. This lasts through a reboot.
This can also be applied to md0 and md126, although i'm not sure i can tell any benefit there.
ie Using a matched size SSD and HDD you can create a RAID1 as normal but then using mdadm cli add a "writemostly" option to the HDD. This causes the kernel to read only from the SSD. ie massive read performance increase.
For example:
echo writemostly > /sys/block/md1/md/dev-sda4/state
Where sda is my HDD and volume1 is stored at md1. This lasts through a reboot.
This can also be applied to md0 and md126, although i'm not sure i can tell any benefit there.
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dstel
- Posts: 19
- Joined: Thu Oct 15, 2020 2:07 am
Re: SSD Cache
SSD caching, when it was working (I got the 5401 issue, see the ticket wasn't very convincing compared to raw array access (and of course, extended to 16GB RAM that acts as a read-only cache anyway).