From: Anand Jain <anand.jain@oracle.com>
To: dsterba@suse.cz, linux-btrfs@vger.kernel.org, clm@fb.com
Subject: Re: [PATCH 1/2] btrfs: create degraded-RAID1 chunks
Date: Tue, 10 May 2016 19:00:09 +0800 [thread overview]
Message-ID: <5731BF39.50009@oracle.com> (raw)
In-Reply-To: <5726EF6B.7010404@oracle.com>
>>> - .devs_min = 2,
>>> + .devs_min = 1,
>> I think we should introduce another way how to determine the lower limit
>> for the degraded mounts. We need the proper raidX constraints and use
>> the degraded limits only if in case of the degraded mount.
>>> .tolerated_failures = 1,
>> Which is exactly the tolerated_failures:
>>
>> degraded_devs_min == devs_min - tolerated_failures
> that is devs_min is actually healthy_devs_min.
>> which works for all raid levels with redundancy.
> But not for RAID5 and RAID6.
> Here is a (simulation?) tool which gives some ready ans.
> I have added devs_min - tolerated_failures to it.
>
> https://github.com/asj/btrfs-raid-cal.git
I have copied the state table from the above repo and
modified to add the above equation.
[x1 = devs_increment * sub_stripes]
[ndevs' = ndevs - ndevs % devs_increment]
[num_stripes = ndevs' * dev_stripes]
[data_stripes = num_stripes / ncopies]
[missing_mirror_dev = x1 - ndevs']
[Y = devs_min - tolerated_failures ]
R10 R1 DUP R0 Sn R5 R6
.sub_stripes = 2, 1, 1, 1, 1, 1, 1
.dev_stripes = 1, 1, 2, 1, 1, 1, 1
.devs_max = 0, 2, 1, 0, 1, 0, 0
.devs_min = 4, 1, 1, 2, 1, 2, 3
.tolerated_fails= 1, 1, 0, 0, 0, 1, 2
.devs_increment = 2, 2, 1, 1, 1, 1, 1
.ncopies = 2, 2, 2, 1, 1, 2, 3
x1 = 4, 2, 1, 1, 1, 1, 1
Y = 3, 0, 1, 2, 1, 1, 1
[ndevs = 9]
ndevs = 9, 9, 9, 9, 9, 9, 9
ndevs' = 8, 2, 1, 9, 9, 9, 9
num_stripes = 8, 2, 2, 9, 1, 9, 9
data_stripes = 4, 1, 1, 9, 1, 8, 7
[ndevs = tolerated_fails + devs_min]
ndevs = 5, 2, 1, 2, 1, 3, 5
ndevs' = 4, 2, 1, 2, 1, 3, 5
num_stripes = 4, 2, 2, 2, 1, 3, 5
data_stripes = 2, 1, 1, 2, 1, 1, 1
[ndevs = devs_min]
ndevs = 3, 1, 1, 2, 1, 2, 3
ndevs' = 2, 0, 1, 2, 1, 2, 3
num_stripes = -, -, 2, 2, 1, 2, 3
data_stripes = -, -, 1, 2, 1, 1, 1
[ndevs = devs_min, with RAID1 patch fix]
ndevs = 3, 1, 1, 2, 1, 2, 3
ndevs' = 3, 1, 1, 2, 1, 2, 3
num_stripes = 3, 1, 2, 2, 1, 2, 3
data_stripes = ?, 1, 1, 2, 1, 1, 1
> I am seeing problem as this:
> RAID5&6 devs_min values are in the context of degraded volume.
> RAID1&10.. devs_min values are in the context of healthy volume.
>
> RAID56 is correct. We already have devs_max to know the number
> of devices in a healthy volumes. RAID1 is devs_min is wrong so
> it ended up being same as devs_max.
Thanks, Anand
next prev parent reply other threads:[~2016-05-10 11:00 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-28 3:06 [PATCH 0/2] [RFC] btrfs: create degraded-RAID1 chunks Anand Jain
2016-04-28 3:06 ` [PATCH 1/2] " Anand Jain
2016-04-29 16:42 ` David Sterba
2016-05-02 6:10 ` Anand Jain
2016-05-10 11:00 ` Anand Jain [this message]
2016-04-28 3:06 ` [PATCH 2/2] revert: Btrfs: don't consider the missing device when allocating new chunks Anand Jain
2016-04-29 16:37 ` [PATCH 0/2] [RFC] btrfs: create degraded-RAID1 chunks David Sterba
2016-05-02 4:12 ` Anand Jain
2016-05-02 5:30 ` Duncan
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